swift234

Do not treat unchecked_addr_cast result as RC-identical to its input.

This is needed to generalize unchecked_addr_cast to cover all cases of
casting address that unchecked_bitwise_cast handles for
values. UnsafePointer can be used to case types that are not RC
identical.

I do not believe this change can interfere with ARC opts, and none of
the regressions I chased turned out to be real. (I also don't have a
test case where this impacts ARC opts.) We can easily get the
original functionality back by adding an unchecked_ref_cast_addr
instruction. This new instruction would be generated by new
unsafeCastReference builtin. This builtin could be used in the stdlib
whenever both sides are RC identical.

Swift SVN r29611