Your comment seems a bit self contradictory to me. You mentioned a strong coupling between runtime and compilers, but then go on giving example of the same comp

Your comment seems a bit self contradictory to me. You mentioned a strong coupling between runtime and compilers, but then go on giving example of the same compilers runtime with different runtime. I suspect that the terminology we are using might be the culprit. Thinking of it as compilers, distribution/package and target might be helpful. Both LLVM and GCC are quite flexible in how they can be packaged and distributed to target various platform. A compiler distribution typically would include a (default) runtime, default options, std libraries and supporting tools (linker,debugger etc... etc...) for each supported target in the case of X-compilation. A distribution is definitely strongly coupled to a host os/configuration. But the compiler proper not really.