Fix a Sema invariant bug that I recently introduced involving
the template instantiation of statement-expressions.

I think it was jyasskin who had a crashing testcase in this area;
hopefully this fixes it and he can find his testcase and check it in.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@154189 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/TreeTransform.h b/lib/Sema/TreeTransform.h
index f16b667..fdb861e 100644
--- a/lib/Sema/TreeTransform.h
+++ b/lib/Sema/TreeTransform.h
@@ -6736,14 +6736,20 @@
 template<typename Derived>
 ExprResult 
 TreeTransform<Derived>::TransformStmtExpr(StmtExpr *E) {
+  SemaRef.ActOnStartStmtExpr();
   StmtResult SubStmt
     = getDerived().TransformCompoundStmt(E->getSubStmt(), true);
-  if (SubStmt.isInvalid())
+  if (SubStmt.isInvalid()) {
+    SemaRef.ActOnStmtExprError();
     return ExprError();
+  }
 
   if (!getDerived().AlwaysRebuild() &&
-      SubStmt.get() == E->getSubStmt())
+      SubStmt.get() == E->getSubStmt()) {
+    // Calling this an 'error' is unintuitive, but it does the right thing.
+    SemaRef.ActOnStmtExprError();
     return SemaRef.MaybeBindToTemporary(E);
+  }
 
   return getDerived().RebuildStmtExpr(E->getLParenLoc(),
                                       SubStmt.get(),