Building gcc-darwin-arm64 fork natively from clang

gistfile1.txt

$ brew install mpfr gmp libmpc
$ git clone https://github.com/iains/gcc-darwin-arm64
$ mkdir build-gcc && cd build-gcc
$ CC=clang CXX=clang++ ../gcc-darwin-arm64/configure \
    --with-gmp=/opt/homebrew/Cellar/gmp/6.2.1 \
    --with-mpfr=/opt/homebrew/Cellar/mpfr/4.1.0 \
    --with-mpc=/opt/homebrew/Cellar/libmpc/1.2.1 \
    --with-native-system-header-dir=/usr/include \
    --with-sysroot=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk \
    --disable-nls \
    --build aarch64-apple-darwin20 \
    --disable-multilib \
    --prefix=/opt/gcc-darwin-arm64
$ CC=clang CXX=clang++ make -j4