[clang][Interp] Only check ComparisonCategoryInfo in C++ (#80131)

Binary operators are also of struct type in C, when assigning. Don't try to get the ComparisonCategoryInfo in that case.

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -464,7 +464,7 @@ bool ByteCodeExprGen<Emitter>::VisitBinaryOperator(const BinaryOperator *BO) {
   // Special case for C++'s three-way/spaceship operator <=>, which
   // returns a std::{strong,weak,partial}_ordering (which is a class, so doesn't
   // have a PrimType).
-  if (!T) {
+  if (!T && Ctx.getLangOpts().CPlusPlus) {
     if (DiscardResult)
       return true;
     const ComparisonCategoryInfo *CmpInfo =

clang/test/Sema/struct-cast.c

@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only %s -verify
+// RUN: %clang_cc1 -fsyntax-only %s -fexperimental-new-constant-interpreter -verify
 // expected-no-diagnostics
 
 struct S {