* builtins.c (expand_builtin_memcmp): Do not use cmpstrnsi
	pattern.
	* doc/md.texi (cmpstrn): Note that the comparison stops if both
	fetched bytes are zero.
	(cmpstr): Likewise.
	(cmpmem): Note that the comparison does not stop if both of the
	fetched bytes are zero.

From-SVN: r177701