Replacing LLVM_ON_WIN32 with just _WIN32

Hi,

LLVM_ON_WIN32 is true exactly when the compiler-set _WIN32 is set. I’d like to just replace LLVM_ON_WIN32 with just _WIN32 everywhere – _WIN32 doesn’t require a custom header file, and we already are inconsistent about which of the two versions we should use in the codebase.

Let me know if you see any problems with this plan, else I’ll do the switch in a week or so.

Nico

This is completed as of http://llvm.org/viewvc/llvm-project?view=revision&revision=331224