[clang] [llvm] [X86][MC] Added support for -msse2avx option in llvm-mc (PR #96860)

[Shengchen Kan via cfe-commits]

================
@@ -5201,6 +5201,10 @@ def mrelax_all : Flag<["-"], "mrelax-all">, Group<m_Group>,
   Visibility<[ClangOption, CC1Option, CC1AsOption]>,
   HelpText<"(integrated-as) Relax all machine instructions">,
   MarshallingInfoFlag<CodeGenOpts<"RelaxAll">>;
+def msse2avx : Flag<["-"], "msse2avx">, Group<m_Group>,
+  Visibility<[ClangOption, CC1Option, CC1AsOption]>,
+  HelpText<"Convert SSE to AVX Instructions">,
----------------
KanRobert wrote:

```suggestion
  HelpText<"Specify that the assembler should encode SSE instructions with VEX prefix">,
```

https://github.com/llvm/llvm-project/pull/96860