[clang] [llvm] [RISCV] Add MIPS extensions (PR #121394)

[Djordje Todorovic via llvm-commits]

djtodoro wrote:

@topperc Thanks for the comments!

> This still isn't broken down enough. We usually like to see assembler support in separate patches from code generation.

I have removed `RISCVLoadStoreOptimizer` Pass, and will add it in a separate PR/commit.

> Missing tests in test/MC/RISCV for the assembler and disassembler

Added.



https://github.com/llvm/llvm-project/pull/121394