clang-cl: pass -debug flag to the linker when compiling with debug info

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207233 91177308-0d34-0410-b5e6-96231b3b80d8
clang-cl: /fallback only applies to C or C++ files

We would previously hit an assert if using /fallback with an .ll file.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207234 91177308-0d34-0410-b5e6-96231b3b80d8