Fix miscompilation of Python on HP-PA/Linux

Fix miscompilation of Python on HP-PA/Linux

This is the miscompilation of Python at -O2 on HP-PA/Linux present
on the mainline and 10 branch, caused by the presence of a call to
__builtin_unreachable () in the middle of a heavily branchy code,
which confuses the reorg pass.

gcc/
	PR rtl-optimization/96015
	* reorg.c (skip_consecutive_labels): Minor comment tweaks.
	(relax_delay_slots): When deleting a jump to the next active
	instruction over a barrier, first delete the barrier if the
	jump is the only way to reach the target label.