[macOS] Compiler should not be hardcoded, as gcc can also be used (and _should_ be used on some platforms)
Current Makefile forces Clang for macOS and FreeBSD, this is undesirable and in certain cases breaking. It is okay to fall back to Clang by default, but provided CC has not been set in the environment and build args.
I guess we could check for a CC environment variable. Note however that gcc on macOS is by default an alias for clang. The gcc toolchain can still be installed manually I suppose.
@chqrlie Yes, gcc (real one) can be used on macOS. (On some legacy versions it is the only working compiler.)
You can use 'make CONFIG_CLANG=' to disable the use of clang on MacOS and BSD. If you have a better solution as a Makefile patch, I'll be happy to look at it.