* expr.c (cmpstr_optab, cmpmem_optab): New.
	* genopinit.c: Initialize them.
	* optabs.h: Declare them.
	* optabs.c (init_optabs): Clear them.
	(prepare_cmp_insn):  Use cmpstr_optab and cmpmem_optab to find
	block memory compare insns, not conditional chains.  Restructure
	the fallback generation of a call to memcmp/bcmp for better
	readability.

From-SVN: r72185