[cfe-dev] Using Clang 5.0.0 RC2 with MSVC dev builds

[Stephan T. Lavavej via cfe-dev]

[Zachary Turner] 
> Double checked the code.  We use the lib path in case the user doesn't specify -libpath.  But, looks like we already have an option for that, -libpath.  
> We need the bin path to find cl.exe (for fallback) and link.exe.
> We also use the deduced include path when trying to find universal CRT, and I'm not sure if that's covered by -imsvc.

Don sent me https://reviews.llvm.org/D36842 which I built and hacked until I came up with https://reviews.llvm.org/D36857 . This works for my x86 dev build (haven't tried x64 yet). I don't know if it's the "right" solution, but hopefully it will be of use.

Since it caches the link.exe path, but doesn't really attempt to fix the underlying issue of path reconstruction, I don't think things like the "fall back to cl.exe" feature would work - but fortunately I never want cl.exe fallback with internal dev builds.

STL