[arcmt] Follow-up for r171484; make sure when adding brackets enclosing case statements,
that the case does not "contain" a declaration that is referenced "outside" of it,
otherwise we will emit un-compilable code.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171828 91177308-0d34-0410-b5e6-96231b3b80d8