[clang] [CIR] Implement folder for VecTernaryOp (PR #142946)

[Andy Kaylor via cfe-commits]

================
@@ -1638,6 +1638,41 @@ LogicalResult cir::VecTernaryOp::verify() {
   return success();
 }
 
+OpFoldResult cir::VecTernaryOp::fold(FoldAdaptor adaptor) {
+  mlir::Attribute cond = adaptor.getCond();
+  mlir::Attribute lhs = adaptor.getLhs();
+  mlir::Attribute rhs = adaptor.getRhs();
+
+  if (mlir::isa_and_nonnull<cir::ConstVectorAttr>(cond) &&
+      mlir::isa_and_nonnull<cir::ConstVectorAttr>(lhs) &&
+      mlir::isa_and_nonnull<cir::ConstVectorAttr>(rhs)) {
----------------
andykaylor wrote:

```suggestion
  if (!mlir::isa_and_nonnull<cir::ConstVectorAttr>(cond) ||
      !mlir::isa_and_nonnull<cir::ConstVectorAttr>(lhs) ||
      !mlir::isa_and_nonnull<cir::ConstVectorAttr>(rhs))
    return {};
```

https://github.com/llvm/llvm-project/pull/142946