objective-C arc: Diagnostic can not say to use bridge
casts with c++ named casts. Change notes to say use
bridge with c-style cast instead. // rdar://12788838


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175850 91177308-0d34-0410-b5e6-96231b3b80d8