Add checkers that detect code-level localizability issues for OS X / iOS:
  - A path sensitive checker that warns about uses of non-localized
    NSStrings passed to UI methods expecting localized strings.
  - A syntax checker that warns against not including a comment in
    NSLocalizedString macros.

A patch by Kulpreet Chilana!

(This is the second attempt with the compilation issue on Windows and
the random test failures resolved.)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@245093 91177308-0d34-0410-b5e6-96231b3b80d8