Problem was that -Wall at the end was resetting -Wstrict-overflow, so
here is the current results for signed overflow warnings (python 2.5
branch SVN), a lot of them :

Parser/acceler.c: In function 'fixstate':
Parser/acceler.c:90: warning: assuming signed overflow does not occur
when changing X +- C1 cmp C2 to X cmp C1 +- C2

Parser/node.c: In function 'PyNode_AddChild':
Parser/node.c:90: warning: assuming signed overflow does not occur when
changing X +- C1 cmp C2 to X cmp C1 +- C2
Parser/node.c:90: warning: assuming signed overflow does not occur when
changing X +- C1 cmp C2 to X cmp C1 +- C2

Parser/firstsets.c: In function 'calcfirstset':
Parser/firstsets.c:71: warning: assuming signed overflow does not occur
when simplifying conditional to constant

Parser/pgen.c: In function 'compile_item':
Parser/pgen.c:268: warning: assuming signed overflow does not occur when
changing X +- C1 cmp C2 to X cmp C1 +- C2
Parser/pgen.c: In function '_Py_pgen':
Parser/pgen.c:454: warning: assuming signed overflow does not occur when
simplifying conditional to constant
Parser/pgen.c:556: warning: assuming signed overflow does not occur when
simplifying conditional to constant
Parser/pgen.c:604: warning: assuming signed overflow does not occur when
simplifying conditional to constant
Parser/pgen.c:611: warning: assuming signed overflow does not occur when
simplifying conditional to constant

Parser/tokenizer.c: In function 'new_string':
Parser/tokenizer.c:175: warning: assuming signed overflow does not occur
when changing X +- C1 cmp C2 to X cmp C1 +- C2
Parser/tokenizer.c: In function 'tok_get':
Parser/tokenizer.c:1163: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Parser/tokenizer.c: In function 'PyTokenizer_Get':
Parser/tokenizer.c:1443: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Parser/tokenizer.c:1443: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Parser/tokenizer.c: In function 'PyTokenizer_FromString':
Parser/tokenizer.c:607: warning: assuming signed overflow does not occur
when changing X +- C1 cmp C2 to X cmp C1 +- C2

Objects/abstract.c: In function 'PyObject_CallMethodObjArgs':
Objects/abstract.c:2038: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Objects/abstract.c:2038: warning: assuming signed overflow does not
occur when simplifying conditional to constant
Objects/abstract.c: In function 'PyObject_CallFunctionObjArgs':
Objects/abstract.c:2038: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Objects/abstract.c:2038: warning: assuming signed overflow does not
occur when simplifying conditional to constant

Objects/intobject.c: In function 'PyInt_FromUnicode':
Objects/intobject.c:394: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2

Objects/listobject.c: In function 'merge_at':
Objects/listobject.c:1595: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Objects/listobject.c:1459: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Objects/listobject.c:1459: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Objects/listobject.c:1595: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2

Objects/longobject.c: In function 'PyLong_FromUnicode':
Objects/longobject.c:1701: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Objects/longobject.c: In function '_PyLong_AsScaledDouble':
Objects/longobject.c:703: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Objects/longobject.c:703: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Objects/longobject.c: In function 'long_sub':
Objects/longobject.c:1978: warning: assuming signed overflow does not
occur when simplifying conditional to constant
Objects/longobject.c: In function 'l_divmod':
Objects/longobject.c:1802: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Objects/longobject.c:1802: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2

Objects/stringobject.c: In function 'string_expandtabs':
Objects/stringobject.c:3331: warning: assuming signed overflow does not
occur when simplifying conditional to constant
Objects/stringobject.c:3339: warning: assuming signed overflow does not
occur when simplifying conditional to constant
Objects/stringobject.c: In function 'string_replace':
Objects/stringobject.c:2509: warning: assuming signed overflow does not
occur when simplifying conditional to constant
Objects/stringobject.c:2509: warning: assuming signed overflow does not
occur when simplifying conditional to constant
Objects/stringobject.c:2509: warning: assuming signed overflow does not
occur when simplifying conditional to constant
Objects/stringobject.c:2509: warning: assuming signed overflow does not
occur when simplifying conditional to constant
Objects/stringobject.c:2672: warning: assuming signed overflow does not
occur when simplifying conditional to constant
Objects/stringobject.c: In function 'string_count':
Objects/stringlib/count.h:24: warning: assuming signed overflow does not
occur when simplifying conditional to constant
Objects/stringlib/count.h:24: warning: assuming signed overflow does not
occur when simplifying conditional to constant

Objects/unicodeobject.c: In function 'unicode_expandtabs':
Objects/unicodeobject.c:5719: warning: assuming signed overflow does not
occur when simplifying conditional to constant
Objects/unicodeobject.c:5727: warning: assuming signed overflow does not
occur when simplifying conditional to constant
Objects/unicodeobject.c: In function 'PyUnicodeUCS4_Compare':
Objects/unicodeobject.c:5376: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Objects/unicodeobject.c:5376: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Objects/unicodeobject.c: In function 'PyUnicodeUCS4_Join':
Objects/unicodeobject.c:4659: warning: assuming signed overflow does not
occur when simplifying conditional to constant

Python/ast.c: In function 'ast_for_genexp':
Python/ast.c:1195: warning: assuming signed overflow does not occur when
simplifying conditional to constant
Python/ast.c:1160: warning: assuming signed overflow does not occur when
simplifying conditional to constant
Python/ast.c: In function 'ast_for_atom':
Python/ast.c:1040: warning: assuming signed overflow does not occur when
simplifying conditional to constant
Python/ast.c:1005: warning: assuming signed overflow does not occur when
simplifying conditional to constant

Python/bltinmodule.c: In function 'builtin_map':
Python/bltinmodule.c:907: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Python/bltinmodule.c:847: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Python/bltinmodule.c:847: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2

Parser/tokenizer.c:1163: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Parser/tokenizer.c: In function 'PyTokenizer_Get':
Parser/tokenizer.c:1443: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
Parser/tokenizer.c:1443: warning: assuming signed overflow does not
occur when changing X +- C1 cmp C2 to X cmp C1 +- C2

Python/getargs.c:994: warning: assuming signed overflow does not occur
when changing X +- C1 cmp C2 to X cmp C1 +- C2
Python/getargs.c:1040: warning: assuming signed overflow does not occur
when changing X +- C1 cmp C2 to X cmp C1 +- C2
Python/getargs.c: In function 'seterror':
Python/getargs.c:357: warning: assuming signed overflow does not occur
when changing X +- C1 cmp C2 to X cmp C1 +- C2

Python/import.c: In function 'PyImport_ExtendInittab':
Python/import.c:3129: warning: assuming signed overflow does not occur
when simplifying conditional to constant

Python/modsupport.c: In function 'va_build_value':
Python/modsupport.c:529: warning: assuming signed overflow does not
occur when simplifying conditional to constant

Python/sysmodule.c: In function 'sys_getframe':
Python/sysmodule.c:650: warning: assuming signed overflow does not occur
when changing X +- C1 cmp C2 to X cmp C1 +- C2

Modules/gcmodule.c: In function 'collect':
Modules/gcmodule.c:767: warning: assuming signed overflow does not occur
when changing X +- C1 cmp C2 to X cmp C1 +- C2

./Modules/_sre.c: In function 'sre_match':
./Modules/_sre.c:1002: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1069: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1086: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1143: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1185: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1214: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1238: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1251: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1277: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1291: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1308: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1395: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1408: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c: In function 'sre_umatch':
./Modules/_sre.c:1002: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1069: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1086: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1143: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1185: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1214: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1238: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1251: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1277: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1291: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1308: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1395: warning: assuming signed overflow does not occur
when simplifying conditional to constant
./Modules/_sre.c:1408: warning: assuming signed overflow does not occur
when simplifying conditional to constant

/packages/python-2.5/Modules/stropmodule.c: In function 'strop_replace':
/packages/python-2.5/Modules/stropmodule.c:1102: warning: assuming
signed overflow does not occur when changing X +- C1 cmp C2 to X cmp C1
+- C2

/packages/python-2.5/Modules/_heapqmodule.c: In function 'heappop':
/packages/python-2.5/Modules/_heapqmodule.c:146: warning: assuming
signed overflow does not occur when changing X +- C1 cmp C2 to X cmp C1
+- C2

/packages/python-2.5/Modules/_hotshot.c: In function 'pack_line_times':
/packages/python-2.5/Modules/_hotshot.c:693: warning: assuming signed
overflow does not occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
/packages/python-2.5/Modules/_hotshot.c: In function 'pack_frame_times':
/packages/python-2.5/Modules/_hotshot.c:706: warning: assuming signed
overflow does not occur when changing X +- C1 cmp C2 to X cmp C1 +- C2

/packages/python-2.5/Modules/binascii.c: In function 'binascii_a2b_base64':
/packages/python-2.5/Modules/binascii.c:320: warning: assuming signed
overflow does not occur when changing X +- C1 cmp C2 to X cmp C1 +- C2
/packages/python-2.5/Modules/binascii.c: In function 'binascii_b2a_uu':
/packages/python-2.5/Modules/binascii.c:287: warning: assuming signed
overflow does not occur when changing X +- C1 cmp C2 to X cmp C1 +- C2

/packages/python-2.5/Modules/parsermodule.c: In function
'validate_subscript':
/packages/python-2.5/Modules/parsermodule.c:2811: warning: assuming
signed overflow does not occur when changing X +- C1 cmp C2 to X cmp C1
+- C2

/packages/python-2.5/Modules/cPickle.c: In function 'Unpickler_noload':
/packages/python-2.5/Modules/cPickle.c:193: warning: assuming signed
overflow does not occur when simplifying conditional to constant
/packages/python-2.5/Modules/cPickle.c:194: warning: assuming signed
overflow does not occur when reducing constant in comparison
/packages/python-2.5/Modules/cPickle.c:4232: warning: assuming signed
overflow does not occur when assuming that (X - c) > X is always false
/packages/python-2.5/Modules/cPickle.c:194: warning: assuming signed
overflow does not occur when assuming that (X - c) > X is always false
/packages/python-2.5/Modules/cPickle.c: In function 'load':
/packages/python-2.5/Modules/cPickle.c:4232: warning: assuming signed
overflow does not occur when assuming that (X - c) > X is always false

/packages/python-2.5/Modules/audioop.c: In function 'audioop_ratecv':
/packages/python-2.5/Modules/audioop.c:1150: warning: assuming signed
overflow does not occur when changing X +- C1 cmp C2 to X cmp C1 +- C2

/packages/python-2.5/Modules/imageop.c: In function 'imageop_dither2grey2':
/packages/python-2.5/Modules/imageop.c:430: warning: assuming signed
overflow does not occur when simplifying conditional to constant

/packages/python-2.5/Modules/_csv.c: In function 'join_append_data':
/packages/python-2.5/Modules/_csv.c:969: warning: assuming signed
overflow does not occur when simplifying conditional to constant

/packages/python-2.5/Modules/expat/xmlparse.c: In function 'getAttributeId':
/packages/python-2.5/Modules/expat/xmlparse.c:5337: warning: assuming
signed overflow does not occur when simplifying conditional to constant

/packages/python-2.5/Modules/dlmodule.c: In function 'dl_call':
/packages/python-2.5/Modules/dlmodule.c:103: warning: assuming signed
overflow does not occur when changing X +- C1 cmp C2 to X cmp C1 +- C2