Fix PR8796.

The problem was that we were asserting the we never added an empty class
to the same offset twice. This is not true for unions, where two members, empty
or not, can have the some offset.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@122633 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/RecordLayoutBuilder.cpp b/lib/AST/RecordLayoutBuilder.cpp
index 34d4a7e..143fc61 100644
--- a/lib/AST/RecordLayoutBuilder.cpp
+++ b/lib/AST/RecordLayoutBuilder.cpp
@@ -216,10 +216,12 @@
   if (!RD->isEmpty())
     return;
 
+  // If we have empty structures inside an union, we can assign both
+  // the same offset. Just avoid pushing them twice in the list.
   ClassVectorTy& Classes = EmptyClassOffsets[Offset];
-  assert(std::find(Classes.begin(), Classes.end(), RD) == Classes.end() &&
-         "Duplicate empty class detected!");
-
+  if (std::find(Classes.begin(), Classes.end(), RD) != Classes.end())
+    return;
+  
   Classes.push_back(RD);
   
   // Update the empty class offset.