swift234

Fix AllocBoxToStack cloning problem described in rdar://problem/19287131.

Recent name mangling changes resulted in AllocBoxToStack cloning the
referenced function of a partial apply once for every reference (i.e. we
would end up with N copies within the cloned function if there were N
references).

Fix this by checking for an already existing function *outside* of the
cloner rather than inside of it.

Swift SVN r24005