Running

gcc -Wl,-R/usr/local/lib,-R/usr/lib  -o python Python/pymath.o Modules/python.o libpython2.7.a -lresolv -lsocket -lnsl -lrt -ldl  -lpthread   -lm

mv build/lib.solaris-2.8-sun4u-2.7/math_failed.so build/lib.solaris-2.8-sun4u-2.7/math.so

seems to have made math module import correctly and work:

bash-2.03$ ./python
Python 2.7 (r27:82500, Nov 23 2010, 14:49:30)
[GCC 3.4.6] on sunos5
Type "help", "copyright", "credits" or "license" for more information.
>>> import math
>>> math.floor(2.4)
2.0


I suppose it's more a workaround than a solution, but hopefully it makes using math module possible and confirms the suggestion there might be something wrong with ar/gcc linking the .a file.