Firstly, this isn't my first attempt at building an LFS system - I've already successfully built LFS 7.8 and LFS 7.8-systemd.
I would like to replace GCC+GlibC with ELLCC, which is Clang/LLVM+musl.
It has a few limitations - the most notable of which is that it currently lacks support for dynamic linking - but the intended end is a cross-compiled (or better yet, compiled on-device) armhf LFS build, as part of an experiment in replacing Android completely with Linux on an old device of mine, so the efficiency of the binaries produced matters (hence the reason I'm interested in using ELLCC.)
The real question is, how would I go about doing this? Simply replacing GCC and GlibC with ELLCC won't even let me get past installing the Linux API headers. I can compile some of the programs from source separately, but they always end up relying on the host system in one way or another.