chicken: support darwin platform (#103748)
Darwin was not included as a supported platform for chicken. However, it compiled and
worked fine after bypassing unsupported platforms.
We make two changes to chicken's derivation. First, we add darwin as a supported
platform.
Second, we set some envvars that force the build to use nix-supplied build
tools. Chicken's Makefile for macOS hardcodes paths to gcc and other build tools
(see
https://code.call-cc.org/cgi-bin/gitweb.cgi?p=chicken-core.git;a=blob;f=Makefile.macosx;h=5d4d9b0aa1bb4c95e1ba7a55f9586fa86ee5034f;hb=317468e4994e6245d787400359726a9fb97d5d60#l31). We
override these envvars to use the wrapped $CC and bintools provided by nix to make
the build pure.
79b78663e5