[clang] [Clang] [Frontend] fix crash on parsing ternary operator with `vector_size` condition (PR #102004)

[Matheus Izvekov via cfe-commits]

================
@@ -6719,6 +6719,16 @@ QualType Sema::CheckVectorConditionalTypes(ExprResult &Cond, ExprResult &LHS,
             : UsualArithmeticConversions(LHS, RHS, QuestionLoc,
                                          ACK_Conditional);
 
+    if (ResultElementTy.isNull()) {
+      Diag(QuestionLoc, diag::err_conditional_vector_mismatched)
+          << LHSType << RHSType;
+      return {};
+    }
----------------
mizvekov wrote:

So we are checking if we are dealing with the same type just above.

If we don't support different types, then the call to `UsualArithmeticConversions` is useless, so it can be removed and this can be further simplified:

```suggestion
    if (!Context.hasSameType(LHSType, RHSType)) {
      Diag(QuestionLoc, diag::err_conditional_vector_mismatched)
          << LHSType << RHSType;
      return {};
    }
    QualType ResultElementTy = Context.getCommonSugaredType(LHSType, RHSType);
```

https://github.com/llvm/llvm-project/pull/102004