LLVM+BSD+musl+Linux

default system toolchain and compiler

LLVM and clang 9.0.0+ (with compiler-rt)

default system linker

LLVM/lld

default system C runtime library

musl

default system C++ runtime library

LLVM/libc++, LLVM/libc++abi, LLVM/libunwind

default system OpenMP library

LLVM/openmp

default system "coreutils"

experimental attempt to bring the BSD utils to Linux

also checkout this project https://github.com/uutils/coreutils

The entire stack is completely GNU-free and (except coreutils) is proven to work. I'm running a GNU-free Gentoo Linux as my daily driver. I get my entire work done there, including but not limited to development, web browsing, chatting with friends, gaming (requires a GNU compatibility layer) and more...

Minor Warning: There is software which hard depends on GNU though which requires portability patches :(

btw I don't use GNU :^)