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

[Lu Weining via cfe-commits]

SixWeining wrote:

> [gcc.gnu.org/onlinedocs/gcc/LoongArch-Options.html](https://gcc.gnu.org/onlinedocs/gcc/LoongArch-Options.html) says
> 
> ‘large (Not implemented yet)’ ‘extreme’ This mode does not limit the size of the code segment and data segment. The -mcmodel=extreme option is incompatible with -fplt, and it requires -mexplicit-relocs=always.
> 
> Is there a psABI defining 'extreme' or 'large'?

Currently there is no definition in psABI except in gcc doc: https://gcc.gnu.org/onlinedocs/gcc/LoongArch-Options.html. Maybe we can define them in next psABI version.

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