[clang][Interp] Fix integral overflow reporting

We need to always do the CCEDiag, the report() is optional.

Author: tbaederr

clang/lib/AST/Interp/Interp.h

@@ -302,15 +302,16 @@ bool AddSubMulHelper(InterpState &S, CodePtr OpPC, unsigned Bits, const T &LHS,
     auto Loc = E->getExprLoc();
     S.report(Loc, diag::warn_integer_constant_overflow)
         << Trunc << Type << E->getSourceRange();
-    return true;
-  } else {
-    S.CCEDiag(E, diag::note_constexpr_overflow) << Value << Type;
-    if (!S.noteUndefinedBehavior()) {
-      S.Stk.pop<T>();
-      return false;
-    }
-    return true;
   }
+
+  S.CCEDiag(E, diag::note_constexpr_overflow) << Value << Type;
+
+  if (!S.noteUndefinedBehavior()) {
+    S.Stk.pop<T>();
+    return false;
+  }
+
+  return true;
 }
 
 template <PrimType Name, class T = typename PrimConv<Name>::T>

clang/test/SemaCXX/enum.cpp

@@ -1,5 +1,9 @@
 // RUN: %clang_cc1 -fsyntax-only -pedantic -std=c++98 -verify -triple x86_64-apple-darwin %s
 // RUN: %clang_cc1 -fsyntax-only -pedantic -std=c++11 -verify -triple x86_64-apple-darwin %s
+
+// RUN: %clang_cc1 -fsyntax-only -pedantic -std=c++98 -verify -triple x86_64-apple-darwin %s -fexperimental-new-constant-interpreter
+// RUN: %clang_cc1 -fsyntax-only -pedantic -std=c++11 -verify -triple x86_64-apple-darwin %s -fexperimental-new-constant-interpreter
+
 enum E { // expected-note{{previous definition is here}}
   Val1,
   Val2