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/interface1.m b/test/ASTMerge/Inputs/interface1.m
index a508bc1..029dad3 100644
--- a/test/ASTMerge/Inputs/interface1.m
+++ b/test/ASTMerge/Inputs/interface1.m
@@ -68,3 +68,8 @@
 @protocol P2 <P0>
 - (float)wibble:(int)a1 second:(int)a2;
 @end
+
+// Forward-declared interfaces
+@class I10, I11;
+@interface I12
+@end