Initial Comment:
Build of Python 2.5 on AIX 5.3 with xlc_r fails with the below error message.

The configure line is:
./configure --with-gcc="xlc_r -q64" --with-cxx="xlC_r -q64" --disable-ipv6 AR="ar -X64"

[...]
building '_ctypes' extension
xlc_r -q64 -DNDEBUG -O -I. -I/sw_install/python-2.5/./Include -Ibuild/temp.aix-5.3-2.5/libffi/include -Ibuild/temp.aix-5.3-2.5/libffi -I/sw_install/python-2.5/Modules/_ctypes/libffi/src -I./Include -I. -I/sw_install/python-2.5/Include -I/sw_install/python-2.5 -c /sw_install/python-2.5/Modules/_ctypes/_ctypes.c -o build/temp.aix-5.3-2.5/sw_install/python-2.5/Modules/_ctypes/_ctypes.o
"build/temp.aix-5.3-2.5/libffi/include/ffi.h", line 221.3: 1506-166 (S) Definition of function ffi_closure requires parentheses.
"build/temp.aix-5.3-2.5/libffi/include/ffi.h", line 221.15: 1506-276 (S) Syntax error: possible missing '{'?
"build/temp.aix-5.3-2.5/libffi/include/ffi.h", line 248.3: 1506-273 (E) Missing type in declaration of ffi_raw_closure.
"build/temp.aix-5.3-2.5/libffi/include/ffi.h", line 251.38: 1506-275 (S) Unexpected text '*' encountered.
"build/temp.aix-5.3-2.5/libffi/include/ffi.h", line 252.23: 1506-276 (S) Syntax error: possible missing identifier?
"build/temp.aix-5.3-2.5/libffi/include/ffi.h", line 251.1: 1506-033 (S) Function ffi_prep_raw_closure is not valid. Function cannot return a function.
"build/temp.aix-5.3-2.5/libffi/include/ffi.h", line 251.1: 1506-282 (S) The type of the parameters must be specified in a prototype.
"build/temp.aix-5.3-2.5/libffi/include/ffi.h", line 254.23: 1506-275 (S) Unexpected text 'void' encountered.
"build/temp.aix-5.3-2.5/libffi/include/ffi.h", line 254.38: 1506-275 (S) Unexpected text ')' encountered.
"build/temp.aix-5.3-2.5/libffi/include/ffi.h", line 257.43: 1506-275 (S) Unexpected text '*' encountered.
"build/temp.aix-5.3-2.5/libffi/include/ffi.h", line 258.28: 1506-276 (S) Syntax error: possible missing identifier?
"build/temp.aix-5.3-2.5/libffi/include/ffi.h", line 257.1: 1506-033 (S) Function ffi_prep_java_raw_closure is not valid. Function cannot return a function.
"build/temp.aix-5.3-2.5/libffi/include/ffi.h", line 257.1: 1506-282 (S) The type of the parameters must be specified in a prototype.
"build/temp.aix-5.3-2.5/libffi/include/ffi.h", line 260.28: 1506-275 (S) Unexpected text 'void' encountered.
"build/temp.aix-5.3-2.5/libffi/include/ffi.h", line 260.43: 1506-275 (S) Unexpected text ')' encountered.
"/sw_install/python-2.5/Modules/_ctypes/ctypes.h", line 71.9: 1506-046 (S) Syntax error.
"/sw_install/python-2.5/Modules/_ctypes/ctypes.h", line 77.26: 1506-195 (S) Integral constant expression with a value greater than zero is required.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes.c", line 2804.31: 1506-068 (E) Operation between types "void*" and "int(*)(void)" is not allowed.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes.c", line 3357.28: 1506-280 (E) Function argument assignment between types "int(*)(void)" and "void*" is not allowed.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes.c", line 3417.42: 1506-022 (S) "pcl" is not a member of "struct {...}".
"/sw_install/python-2.5/Modules/_ctypes/_ctypes.c", line 4749.67: 1506-280 (E) Function argument assignment between types "void*" and "void*(*)(void*,const void*,unsigned long)" is not allowed.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes.c", line 4750.66: 1506-280 (E) Function argument assignment between types "void*" and "void*(*)(void*,int,unsigned long)" is not allowed.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes.c", line 4751.69: 1506-280 (E) Function argument assignment between types "void*" and "struct _object*(*)(const char*,long)" is not allowed.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes.c", line 4752.64: 1506-280 (E) Function argument assignment between types "void*" and "struct _object*(*)(void*,struct _object*,struct _object*)" is not allowed.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes.c", line 4754.70: 1506-280 (E) Function argument assignment between types "void*" and "struct _object*(*)(const unsigned int*,int)" is not allowed.
building '_ctypes_test' extension
xlc_r -q64 -DNDEBUG -O -I. -I/sw_install/python-2.5/./Include -I./Include -I. -I/sw_install/python-2.5/Include -I/sw_install/python-2.5 -c /sw_install/python-2.5/Modules/_ctypes/_ctypes_test.c -o build/temp.aix-5.3-2.5/sw_install/python-2.5/Modules/_ctypes/_ctypes_test.o
"/sw_install/python-2.5/Modules/_ctypes/_ctypes_test.c", line 61.1: 1506-046 (S) Syntax error.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes_test.c", line 68.1: 1506-046 (S) Syntax error.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes_test.c", line 75.1: 1506-046 (S) Syntax error.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes_test.c", line 320.9: 1506-009 (S) Bit-field M must be of type signed int, unsigned int or int.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes_test.c", line 320.9: 1506-009 (S) Bit-field N must be of type signed int, unsigned int or int.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes_test.c", line 320.9: 1506-009 (S) Bit-field O must be of type signed int, unsigned int or int.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes_test.c", line 320.9: 1506-009 (S) Bit-field P must be of type signed int, unsigned int or int.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes_test.c", line 320.9: 1506-009 (S) Bit-field Q must be of type signed int, unsigned int or int.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes_test.c", line 320.9: 1506-009 (S) Bit-field R must be of type signed int, unsigned int or int.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes_test.c", line 320.9: 1506-009 (S) Bit-field S must be of type signed int, unsigned int or int.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes_test.c", line 371.1: 1506-046 (S) Syntax error.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes_test.c", line 371.31: 1506-045 (S) Undeclared identifier get_last_tf_arg_s.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes_test.c", line 372.1: 1506-046 (S) Syntax error.
"/sw_install/python-2.5/Modules/_ctypes/_ctypes_test.c", line 372.31: 1506-045 (S) Undeclared identifier get_last_tf_arg_u.
[...]