[-fcompare-debug] retain insn locations when turning dbr seq into return

[-fcompare-debug] retain insn locations when turning dbr seq into return

A number of -fcompare-debug errors on sparc arise as we split a dbr
SEQUENCE back into separate insns to turn the branch into a return.
If we just take the location from the PREV_INSN, it might be a debug
insn without INSN_LOCATION, or an insn with an unrelated location.
But that's silly: each of the SEQUENCEd insns is still an insn with
its own INSN_LOCATION, so use that instead, even though some may have
been adjusted while constructing the SEQUENCE.

for  gcc/ChangeLog

	* reorg.c (make_return_insns): Reemit each insn with its own
	location.

From-SVN: r255948