Don't suppress access-control or invalid-type diagnostics from a

declarator just because we were able to build an invalid decl
for it.  The invalid-type diagnostics, in particular, are still useful
to know, and may indicate something about why the decl is invalid.

Also, recover from an illegal pointer/reference-to-unqualified-retainable
type using __strong instead of __autoreleasing;  in general, a random
object is much more likely to be __strong, so this avoids unnecessary
cascading errors in the most common case.

llvm-svn: 149074