Log Message:
py-scipy: Lower GCC_REQD requirement to 13.

I don't like this change, but the previous setting of 14 is far far worse,
and it is unclear why it was made when this project continues to state that
GCC 9 is sufficient.  GCC 13 certainly builds it absolutely fine.

I would recommend that those with even older compilers test them and make
any necessary changes to continue to lower the value, or better yet, convert
it to USE_*_FEATURES.