[ASan Win] Fix a couple of warnings in tests and enable -WX

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@209887 91177308-0d34-0410-b5e6-96231b3b80d8
[Sanitizers Win] Move duplicate Windows-specific compiler flags to a common CMake variable

Reviewed at http://reviews.llvm.org/D3952

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@209889 91177308-0d34-0410-b5e6-96231b3b80d8