[llvm] [cmake] Add possibility to use ChooseMSVCCRT.cmake when include LLVM library
Modify LLVMConfig to produce LLVM_USE_CRT variables in build-directory. It helps to set the same compiler debug options like in builded library.
Excuse me, I have add to reviewers people, who review this file. Add relative people, if needed, please.
This change helps to build library and user-tool with same flags.
lgtm, it's in the LLVM_ namespace, so it couldn't hurt to record it.