[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.

[David Ziman]

Hello, I have created a patch located here: [[ http://reviews.llvm.org/D4061 | http://reviews.llvm.org/D4061 ]]

Please review at your convenience.

Summary:
This patch prevents Clang from calling link.exe that happens to be in the PATH environment variable in favor of the one where MSVC is installed. Clang would commonly call upon "C:\gnuwin32\bin\link.exe"; which is a tool for creating "links" between files on a filesystem, which is probably not the expected behavior.

This patch also adds support for calling on 64-bit MSVC tools when the host process is 64-bit.

This patch also extends the support for implicitly finding MSVC 11.0 includes in the same way it does for MSVC 9.0 and 10.0. It also corrects the path for 64-bit machines.

http://reviews.llvm.org/D4061