[clang] [clang] Add GCC-compatible code model names for sparc64 (PR #79485)

[via cfe-commits]

koachan wrote:

> Have you checked whether these code models are actually implemented and how complete they are? For example, if one model is very far from complete, perhaps we should be honest and say it is unsupported.

All three I listed is implemented in some capacity; the one that is the most well-exercised, so to say, is the `medmid`/`medium` one, given that it is the default one used by LLVM. For the rest, there's a couple tests at `llvm/test/CodeGen/SPARC/{blockaddr,constpool,globals,func-addr}.ll` but while the tests seem to be okay, I haven't really tried using them to do some bigger-scale compiles...

https://github.com/llvm/llvm-project/pull/79485