[ARC] Fix errors in arc_ifcvt.

[ARC] Fix errors in arc_ifcvt.

The arc_ifcvt procedure is removing a label even when it is used by
another jump.  This patch fixes dg.exp/pr31507-1.c.

gcc/
2017-07-10  Claudiu Zissulescu  <claziss@synopsys.com>

	* config/arc/arc.c (arc_ifcvt): Remove use of merge_blocks call.
	(arc_ccfsm_advance): Fix checking for delay slots.
	(arc_reorg): Add rtl dump after each call to arc_ifcvt

From-SVN: r251588