swift234

Change SILCloner to be able to remap additional non-instruction based SILValues such as SILUndef.

Previously we only supported SILArguments. In the process of changing this I
noticed that our densemap implementation for SILValues only hashes the wrapped
ValueBase instead of hash combining that hash with a hash of the result number.

The main use case for this is to enable the insertion of a Builtin.trap + RAUW
SILUndef of uses of an unconditional_checked_cast that is invalid after
specialization.

rdar://16490450

Swift SVN r15747