A Tale of Two Toolchains and glibc

Over the past few years, the LLVM toolchain has seen increasing development and adoption alongside the older, more established GNU toolchain. The emergence of this new two major toolchain world is bringing challenges and questions for projects that need to support both, in particular the GNU C library (glibc), which only supports GCC.

Is it worth it to fix glibc (and other projects which support only GCC) to build with LLVM? Is it better to just replace them with alternatives already supporting LLVM? Is it best to use both GCC and LLVM, each for their respective supported projects?