ObjectiveC. Continuing implementation of objc_bridge_related
attribute in sema and issuing a variety of diagnostics lazily 
for misuse of this attribute (and what to do) when converting 
from CF types to ObjectiveC types (and vice versa).
// rdar://15499111


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@196629 91177308-0d34-0410-b5e6-96231b3b80d8