make some diagnostics more terse, update testcases.

Fix Sema::ActOnInstanceMessage to correctly do things in terms of canonical 
types, fixing bogus errors like:

NSDistantObject.m:10383:120: error: bad receiver type 'typeof((id<NSMutableCopying>)self)'
    id mess = ({ id __inv__ = ((void *)0); id __mb__ = _NSMessageBuilder((id <NSMutableCopying>)self, &__inv__); (void)[(__typeof__((id <NSMutableCopying>)self))__mb__ mutableCopyWithZone:((void *)0)]; if (!objc_collecting_enabled()) object_dispose(__mb__); __inv__; });

llvm-svn: 46633