Could you add support for systems with no gcc

I use the llvm/musl profile and it fails on the check in gcc_check in auto-cpu-optimization.sh you could easily find it for clang with something like: ```clang -### -march=native -E - </dev/null 2>&1 | grep -Po -m 1 'target-cpu"[[:space:]]"\K\w+'``` which also returns the target cpu, thanks