[ASan tests] Also define USED/UNUSED in lib/sanitizer_common/sanitizer_internal_defs.h if Clang is used on Windows

Otherwise we end up with macro redefinition warnings

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@208571 91177308-0d34-0410-b5e6-96231b3b80d8