clang/test/CodeGenCXX/debug-info-namespace.cpp: Suppress this also on msys, for now since r193116.

Clang confuses among dosish paths. In this case, "Input/foo.cpp" and "Input\foo.cpp" cannot be unified.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193456 91177308-0d34-0410-b5e6-96231b3b80d8