[clang] [Headers][X86] Allow pmuludq/pmuldq to be used in constexpr (PR #153293)

[Simon Pilgrim via cfe-commits]

================
@@ -907,6 +907,7 @@ __m256i test_mm256_mul_epi32(__m256i a, __m256i b) {
   // CHECK: mul <4 x i64> %{{.*}}, %{{.*}}
   return _mm256_mul_epi32(a, b);
 }
+TEST_CONSTEXPR(match_v8si(_mm256_mul_epi32((__m256i)(__v8si){+1, -2, +3, -4, +5, -6, +7, -8}, (__m256i)(__v8si){-16, -14, +12, +10, -8, +6, -4, +2}), -16, -1, 36, 0, -40, -1, -28, -1));
----------------
RKSimon wrote:

match_v8si?

https://github.com/llvm/llvm-project/pull/153293