I would very much appreciate any new compiler be compatible with the
standard Windows debuggers (windbg primarily, but I imagine most
contributors would like it to keep working from VS).
Last I heard, clang is fine as a compiler for debugging if you use the
MSVC linker to generate debug info, though it still isn't as complete as
MSVC (ultimately by definition, since MSVC is the
standard-by-implementation for this stuff). And I've got no idea
how/whether link-time optimisation works when you mix tools, but I'd
have to assume it doesn't.
Switching compiler may prevent me from being able to analyse crash
reports (and by me, I mean the automated internal tools that do it for
me), and certainly parts of the Windows build rely on MSVC-specific
functionality right now (not in the main DLL) so we'd end up needing
both for a full build.
Also, just to put it out there, I'm not volunteering to rewrite the
build system :) If the steering council signs off on switching, I won't
block it, but I have more interesting things to work on.