__declspec(uuid) is only supported for C++ code according to MSDN (as well as behaviorally in MSVC). This adds a generic diagnostic that we use for uuid, and can use for some other attributes as well, and adds a testcase.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@195580 91177308-0d34-0410-b5e6-96231b3b80d8