[clang] Evaluate constant initializers in C as well

Author: tbaederr

clang/lib/Sema/SemaDecl.cpp

@@ -14481,7 +14481,8 @@ void Sema::CheckCompleteVariableDeclaration(VarDecl *var) {
     // do this lazily, because the result might depend on things that change
     // later, such as which constexpr functions happen to be defined.
     SmallVector<PartialDiagnosticAt, 8> Notes;
-    if (!getLangOpts().CPlusPlus11 && !getLangOpts().C23) {
+    if (getLangOpts().CPlusPlus && !getLangOpts().CPlusPlus11 &&
+        !getLangOpts().C23) {
       // Prior to C++11, in contexts where a constant initializer is required,
       // the set of valid constant initializers is described by syntactic rules
       // in [expr.const]p2-6.