[clang] Remove an incorrect assertion in ConstantFoldAttrs

Evaluating the attribute expression can be successful without resulting
in a value. Namely, when the expression is of type void.

Author: tbaederr

clang/lib/Sema/SemaAttr.cpp

@@ -439,8 +439,8 @@ bool Sema::ConstantFoldAttrArgs(const AttributeCommonInfo &CI,
         Diag(Note.first, Note.second);
       return false;
     }
-    assert(Eval.Val.hasValue());
-    E = ConstantExpr::Create(Context, E, Eval.Val);
+    if (Eval.Val.hasValue())
+      E = ConstantExpr::Create(Context, E, Eval.Val);
   }
 
   return true;

clang/test/SemaCXX/attr-annotate.cpp

@@ -134,3 +134,7 @@ constexpr int foldable_but_invalid() {
 template <typename T> [[clang::annotate()]] void f2() {}
 // expected-error@-1 {{'annotate' attribute takes at least 1 argument}}
 }
+
+namespace test5 {
+  void bir [[clang::annotate("B", (void)1)]] ();
+}