fab/forwprop: Move memcmp->memcmp_eq to forwprop

fab/forwprop: Move memcmp->memcmp_eq to forwprop

This moves from the memcmp->memcmp_eq to forwprop by
checking PROP_last_full_fold.

Note this means at -Og, we no longer optimize some
memcmp. That will be fixed when I exchange fab/copyprop
for a (late) forwprop.

Bootstrapped and tested on x86_64-linux-gnu.

gcc/ChangeLog:

	* tree-ssa-ccp.cc (optimize_memcmp_eq): Remove.
	(pass_fold_builtins::execute): Remove handling of memcmp.
	* tree-ssa-forwprop.cc (simplify_builtin_memcmp): Add folding
	of memcmp to memcmp_eq for PROP_last_full_fold.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>