impl_reg_cp() doesn't apply register offsets
Remove phi-merge out_comment()
Handle ?: GNU expression code gen
Handle control transfer where the basic block changes

In some cases the block we start on isn't the block we end on, so we
need the up-to-date block for the call to out_ctrl_merge().

Also assert that we don't transfer from the same block twice.
blk_terminate_undef() for setting BLK_TERMINAL
Bring in x86 impl_branch on V_CONST_I and V_LBL/REG_SPILT