Fix a crash in the diangostic code in EvalConstant.  PR12043.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@151100 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index 4ae5ab4..5420876 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -538,8 +538,10 @@
                                  = diag::note_invalid_subexpr_in_const_expr,
                                unsigned ExtraNotes = 0) {
       // Don't override a previous diagnostic.
-      if (!EvalStatus.Diag || !EvalStatus.Diag->empty())
+      if (!EvalStatus.Diag || !EvalStatus.Diag->empty()) {
+        HasActiveDiagnostic = false;
         return OptionalDiagnostic();
+      }
       return Diag(Loc, DiagId, ExtraNotes);
     }