http://lists.gnu.org/archive/html/emacs-devel/2015-02/msg004...

Speking as the original author of GUD, I'm in favor of it supporting
LLVM and everything else imaginable.  But I hadn't been planning to
weigh in on the question until I realize that Richard and everyone
else may be carrying around a false premise: namely, that GCC's
dominance in its functional category *can* be preserved.

I'm pretty sure this is not true.  If the clang/LLVM people decide
they want to eat GCC's lunch, they *will* do it.  The reason has
nothing to do with any philosophical issue but merely the fact that
compiler technology has advanced significantly in ways that GCC is not
well positioned to exploit.  The clang/LLVM people have both a
clean-sheet technology advantage and Apple's money to fund a
high-quality implementation with; FSF cannot match either.

Already my own experiments suggest that LLVM is a superior compiler,
by every metric I know of, at least in deployments that don't require
bug-for-bug compatibility with GCC.  If GCC were to vanish from
existence tomorrow I'm not sure I myself would be even seriously
inconvenienced.  CC=clang in one dotfile; problem solved, done.