Revert "libclang: fix a bug in processing invalid arguments, introduced in r201249,"

Reverting commit (201346) for now, because it is breaking our internal builds.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201373 91177308-0d34-0410-b5e6-96231b3b80d8
Revert "[CMake] Disable libclangTests.exe on win32 for now."

Because I also reverted the original commit that required this change.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201374 91177308-0d34-0410-b5e6-96231b3b80d8