[clang] [Clang] Add __builtin_selectvector and use it for AVX512 intrinsics (PR #91306)

[Aaron Ballman via cfe-commits]

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@@ -1176,6 +1176,12 @@ def ConvertVector : Builtin {
   let Prototype = "void(...)";
 }
 
+def SelectVector : Builtin {
+  let Spellings = ["__builtin_selectvector"];
+  let Attributes = [NoThrow, Const, CustomTypeChecking];
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AaronBallman wrote:

Should this also be constexpr?

https://github.com/llvm/llvm-project/pull/91306