[clang] [llvm] [clang] Support -Wa, options -mmsa and -mno-msa (PR #99615)

[Fangrui Song via cfe-commits]

================
@@ -5337,9 +5337,13 @@ def mmadd4 : Flag<["-"], "mmadd4">, Group<m_mips_Features_Group>,
 def mno_madd4 : Flag<["-"], "mno-madd4">, Group<m_mips_Features_Group>,
   HelpText<"Disable the generation of 4-operand madd.s, madd.d and related instructions.">;
 def mmsa : Flag<["-"], "mmsa">, Group<m_mips_Features_Group>,
-  HelpText<"Enable MSA ASE (MIPS only)">;
+  Visibility<[ClangOption, CC1AsOption]>,
----------------
MaskRay wrote:

See how --crel --no-crel is handled. Add a bool variable and only add `-mmsa` when the variable is true.

https://github.com/llvm/llvm-project/pull/99615