[clang] [Clang] disallow selectany on non-global-variable declarations (PR #189641)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> I guess I don't know which language level nuance should be used for distinguishing these cases then...

Same. :-)

We can't break system headers, and I doubt Microsoft will break them either, so this is a (narrow) case where I think we should just accept what Microsoft accepts despite the documentation on MSDN; we can update our own docs to be a bit more nuanced if we'd like, too.

https://github.com/llvm/llvm-project/pull/189641