Speculative fix for a mod_python build issue on OSX, which is
caused by '-arch i386 -arch x86_64' in the final PYTHON_CFLAGS.

Filter both flags and hope OSX's universal binary toolchain is smart enough
to choose a sane default.

Reported-by: neilp9 in #freeswitch @ irc.freenode.net
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>