Added LLVM_FALLTHROUGH to address warning: this statement may fall through. NFC.

llvm-svn: 304650
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 29d970e..34c4d26 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -6240,6 +6240,8 @@
       S += "{objc_class=}";
       return;
     }
+    // TODO: Double check to make sure this intentially falls through.
+    LLVM_FALLTHROUGH;
   }
   
   case Type::ObjCInterface: {