Fix r162835 as per Richard's comments.

VisitVarDecl should return Error(E), and we should test that the address
of a TLS var can't be used as a constexpr.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@162837 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index 6b88246..ac21b46 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -2833,7 +2833,7 @@
 
 bool LValueExprEvaluator::VisitVarDecl(const Expr *E, const VarDecl *VD) {
   if (VD->isThreadSpecified())
-    return false;
+    return Error(E);
   if (!VD->getType()->isReferenceType()) {
     if (isa<ParmVarDecl>(VD)) {
       Result.set(VD, Info.CurrentCall->Index);