Building on darwin_arm64

[amdiggs]

I finally succeeded in building lib quip on darwin_arm64_gfortran. The issue I was having was that the default gcc was clang-1400 from my Xcode toolchain. changing CC in Makefile.inc did not work; however, editing Makefile.darwin_arm64_gfortran did. I just wanted to put this out in case others run into this issue. I realize this is not best practice so I would suggest cp Makefile.darwin_arm64_gfortran arch/Makefile.${my_mac} and then make sure that CC is set to find some gnu version, e.g CC = gcc-#, which will find the gcc-# in op/homebrew/bin/ for me it was gcc-13. Cheers, Thank you to all the contributors for your hard work in keeping this amazing project going.