combine: Emit a barrier after unconditional trap (PR78607)

After an unconditional trap there should be a barrier.  In most cases
one is automatically inserted, but not if the trap is the final insn in
the instruction stream.  We need to emit one explicitly.


	PR rtl-optimization/78607
	* combine.c (try_combine): Emit a barrier after a unconditional trap.

gcc/testsuite/
	PR rtl-optimization/78607
	* gcc.c-torture/compile/pr78607.c: New testcase.

From-SVN: r243092