[PATCH] Modifies Windows toolchain to prefer link.exe from the MSVC folder rather than PATH and extends capability to implicitly find MSVC 11.0 includes and tools.

[Reid Kleckner]

IMO we have to trust PATH before we start looking in hardcoded places.  The expectation is that the user will be running clang from a vcvars.bat shell, which is one that has INCLUDE, LIB, and PATH all set to point to the version of VS they wanted, which could be one of the many CTPs that we don't have listed here.

This is a real use case, it's how I test Clang with different versions of VS.  :)

http://reviews.llvm.org/D4061