building extension on MacOS with g++

[duanhuaiyu]

I have installed gcc-11 on my Mac. When I tried to build an extension using the command CC=gcc-11 CXX=g++-11 pip install -e ., I received the error gcc-11: error: unrecognized command-line option '-stdlib=libc++'. It seems that pybind11.setup_helpers.Pybind11Extension always adds the flag -stdlib=libc++ if the OS is Darwin. Maybe it should also check the compiler?