Fix <rdar://problem/6697053> instance variable is protected.

Fix <rdar://problem/6697053> instance variable is protected.

Treat @package the same as @public. The documentation for @package says it is analogous to private_extern for variables/functions. Fully implementing this requires some kind of linker support (so access is denied to code outside the classes executable image). I don't believe GCC fully implements this semantic. Will discuss with Fariborz offline.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@67755 91177308-0d34-0410-b5e6-96231b3b80d8