Fix mypyc build errors on newer manylinux2014_x86_64 images (#3272)
Fix mypyc build errors on newer manylinux2014_x86_64 images (#3272)

Make sure `gcc` is installed in the build env

The mypyc build requires `gcc` to be installed even if it's being built with `clang`, otherwise `clang` fails to find `libgcc`.
psf/black