Test that macros can be applied to imported Objective-C declarations

These currently end up as "open", which is incorrect (we need to make them
"final"). This cannot be addressed until we pass the lexical context
down to the macro, which is currently... a bit tricky.

test/Inputs/clang-importer-sdk/usr/include/completion_handler_globals.h

@@ -7,3 +7,14 @@ typedef struct SlowComputer {
 void computer_divide(const SlowComputer *computer, double x, double y, void (* _Nonnull completionHandler)(double x))
   __attribute__((swift_attr("@macro_library.AddAsync")))
   __attribute__((swift_name("SlowComputer.divide(self:_:_:completionHandler:)")));
+
+
+#if __OBJC__
+@import Foundation;
+
+@interface Computer: NSObject
+-(void)multiply:(double)x by:(double)y afterDone:(void (^ _Nonnull)(double x))afterDone
+  __attribute__((swift_attr("@macro_library.AddAsync")))
+  __attribute__((swift_async(none)));
+@end
+#endif