[rjsw]

LLVM doesn't support all the CPU architectures that GCC does, ones missing include 68k, VAX and SH3.

[ndesaulniers]

LLVM recently got a m68k backend. It's still marked experimental, so distros likely aren't enabling it yet. But it's seeing active developments from hobbyists. Main author of the m68k just had a book on LLVM published.