The logic for handling the sinking of COPY instructions was generating
different code when building with debug flags.
The original code did not take into consideration debug instructions. This
resulted in the registers in the DBG_VALUE instructions being treated as used,
and prevented the COPY from being sunk. This patch avoids analyzing debug
instructions when trying to sink COPY instructions.
This patch also creates a routine from the code in MachineSinking::SinkInstruction to
perform the logic of sinking an instruction along with its debug instructions.
This functionality is used in multiple places, including the code for sinking COPY instrs.