Glibc finally accepted the memmem speedup code, bugzilla #5514. * doc/glibc-functions/memmem.texi (memmem): Mention last broken glibc version. * doc/glibc-functions/strcasestr.texi (strcasestr): Likewise. * doc/posix-functions/strstr.texi (strstr): Likewise. * lib/str-two-way.h (MAX): Sychronize with glibc. Signed-off-by: Eric Blake <ebb9@byu.net>