Make -fstandalone-debug and -flimit-debug-info available in clang-cl

Our limited debug info optimizations are breaking down at DLL
boundaries, so we're going to evaluate the size impact of these
settings, and possibly change the default.

Users should be able to override our settings, though.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@281056 91177308-0d34-0410-b5e6-96231b3b80d8