[clang] [CIR] Upstream gather instrinsics (PR #169157)

[Andy Kaylor via cfe-commits]

================
@@ -77,3 +77,99 @@ __m512i test_mm512_undefined_epi32(void) {
   // OGCG: ret <8 x i64> zeroinitializer
   return _mm512_undefined_epi32();
 }
+
+__m256 test_mm512_i64gather_ps(__m512i __index, void const *__addr) {
+  // CHECK-LABEL: test_mm512_i64gather_ps
----------------
andykaylor wrote:

You need to replace `CHECK` with `CIR` in these changes. Can you also add LLVM and OGCG checks?

https://github.com/llvm/llvm-project/pull/169157