[clang] [Headers][X86] Enable constexpr handling for MMX/SSE/AVX/AVX512 avg intrinsics (PR #157464)

[Bhasawut Singhaphan via cfe-commits]

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@@ -24,6 +24,7 @@ typedef float __m128_u __attribute__((__vector_size__(16), __aligned__(1)));
 /* Unsigned types */
 typedef unsigned int __v4su __attribute__((__vector_size__(16)));
 typedef unsigned short __v8hu __attribute__((__vector_size__(16)));
+typedef unsigned char __v16qu __attribute__((__vector_size__(16)));
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markbhasawut wrote:

Should I add `__v16qu` unsigned type to the mmintrin.h for handling this issue instead? @RKSimon 

https://github.com/llvm/llvm-project/pull/157464