NSString is loaded from the DWARF, which doesn't have the concept of protocols.
When this is used with the NSMutableDictionary type from Objective-C modules,
this produces errors of the form
error: cannot initialize a parameter of type 'id<NSCopying> _Nonnull' with an rvalue of type 'NSString *'
We're aware of these problems and have an internal bug report filed
(<rdar://problem/32777981>)
llvm-svn: 305424