bpo-46576: bpo-46524: Disable compiler optimization within test_peg_generator. (#31015)

Disable compiler optimization within test_peg_generator.

This speed up test_peg_generator by always disabling compiler
optimizations by using -O0 or equivalent when the test is building its
own C extensions.

A build not using --with-pydebug in order to speed up test execution
winds up with this test taking a very long time as it would do
repeated compilation of parser C code using the same optimization
flags as CPython was built with.

This speeds the test up 6-8x on gps-raspbian.

Also incorporate's #31017's win32 conditional and flags.

Co-authored-by: Kumar Aditya kumaraditya303