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

[Fangrui Song via cfe-commits]

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+// RUN: %clang -### -c -march=x86-64 -msse2avx %s 2>&1 | FileCheck %s
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MaskRay wrote:

Merge this into `sse2avx.c` using `-x assembler`

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