[clang] [Driver] Support -mcmodel= for LoongArch (PR #72514)

[Xi Ruoyao via cfe-commits]

xry111 wrote:

> And AFAIK, gcc side doesn't plan to implement the "large" code model.

Why did we distinguish "large" and "extreme" in the first place?  If we don't need a different "large" code model then I guess we should make it an alias of "extreme" for GCC too.

https://github.com/llvm/llvm-project/pull/72514