xtensa: Revise complex hard register clobber elimination

xtensa: Revise complex hard register clobber elimination

In the previously posted patch
"xtensa: Make complex hard register clobber elimination more robust and accurate",
the check code for insns that refer to the [DS]Cmode hard register before
it is overwritten after it is clobbered is incomplete.  Fortunately such
insns are seldom emitted, so it didn't matter.

This patch fixes that for the sake of completeness.

gcc/ChangeLog:

	* config/xtensa/xtensa.md:
	Fix exit from loops detecting references before overwriting in the
	split pattern.