swift234

Remove the return value of ArgumentInitVisitor, nothing consumes it.
Doing so makes it plain that the empty tuple case doesn't need to 
synthesize a tupleinst to return.  Eliminating this gets rid of the
weird dead empty tuple you may have seen get dropped in the prolog
of functions taking no arguments.

Also, push around RValue handling a bit in ArgumentInitVisitor, NFC
for this part.



Swift SVN r12230