old_insns_match_p just tests whether two instructions are
similar enough to merge.  With insn_callee_abi it makes more
sense to compare the ABIs directly.

2019-09-30  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* cfgcleanup.c (old_insns_match_p): Compare the ABIs of calls
	instead of the call-clobbered sets.

From-SVN: r276314