This was a problem for people who write 'return(result);'

Also fix ARCMT's corresponding code, though there's no test case for this
because implicit casts like this are rejected by the migrator for being
ambiguous, and explicit casts have no problem.

<rdar://problem/11577346>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158130 91177308-0d34-0410-b5e6-96231b3b80d8