In ARC, reclaim all return values of retainable type, not just those

In ARC, reclaim all return values of retainable type, not just those
where we have an immediate need of a retained value.

As an exception, don't do this when the call is made as the immediate
operand of a __bridge retain.  This is more in the way of a workaround
than an actual guarantee, so it's acceptable to be brittle here.

rdar://problem/9504800

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@134605 91177308-0d34-0410-b5e6-96231b3b80d8