[clang] [Clang] Add __ugly__ spelling for the msvc attribute scope (PR #113765)

[Nikolas Klauser via cfe-commits]

philnik777 wrote:

@AaronBallman I'm not _super_ worried about these specific cases, but I'd like to know how to proceed with `msvc` attributes we'd like to use in libc++ generally. e.g. `msvc::intrinsic` would be quite nice and doesn't actually need to be bound to the MSVC ABI. Also, as more and more attributes can't be _Uglified due to Microsoft not feeling like it there will inevitably be a clash somewhere. I'd also be fine with not providing anything for MSVC-only attributes but providing an alternate spelling for attributes that are useful outside the MSVC ABI. It'd suck having to work around that my not using the obviously correct tool `__has_attribute(msvc::no_unique_address)` though.

https://github.com/llvm/llvm-project/pull/113765