Fix Windows legacy LLVM build
Fix Windows legacy LLVM build

The os.hpp header gets added to the include path of legacy llvm via the compiler lib. Having "windows.h" included causes a lot conflicts with LLVM headers, as they forward declare many Windows types. Best to not include it here.

Change-Id: I60c44a8d28660368f1a4a95741e1053ef3528fa1

ROCm-Developer-Tools/ROCclr,ROCm-Developer-Tools/ROCclr