combine: Make code after a new trap unreachable (PR78342)

combine: Make code after a new trap unreachable (PR78342)

Combine can turn a conditional trap into an unconditional trap.  If it
does that it should make the code after it unreachable (an unconditional
trap should be the last insn in its bb, and that bb has no successors).

This patch seems to work.  It is hard to be sure, this is very hard to
trigger.  Quite a few other passes look like they need something similar
as well, but I don't see anything else handling it yet either.

	PR rtl-optimization/78342
	* combine.c: Include "cfghooks.h".
	(try_combine): If we create an unconditional trap, break the basic
	block in two just after it, and remove the edge between; also, set
	the *new_direct_jump_p flag so that cleanup_cfg is run.

From-SVN: r242947