Implement import of forward declarations of Objective-C classes

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@96554 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/ASTMerge/Inputs/interface2.m b/test/ASTMerge/Inputs/interface2.m
index d79f77d..30de981 100644
--- a/test/ASTMerge/Inputs/interface2.m
+++ b/test/ASTMerge/Inputs/interface2.m
@@ -67,3 +67,8 @@
 @protocol P2 <P0>
 - (float)wibble:(int)a1 second:(int)a2;
 @end
+
+// Forward-declared interface
+@class I12, I10;
+@interface I11
+@end