MFC r283584:

Relnotes: yes

r283584 (by emaste):

memmem(3): empty little string matches the beginning of the big string

This function originated in glibc, and this matches their behaviour
(and NetBSD, OpenBSD, and musl).

An empty big string (arg "l") is handled by the existing
l_len < s_len test.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

- ANSIfy function definitions
- use nul when we are looking for a terminating character where appropriate

Approved by: imp

Add the function memmem(3) as found in glibc and others.
It is the binary equivalent to strstr(3).

void *memmem(const void *big, size_t big_len,
const void *little, size_t little_len);

Submitted by: Pascal Gloor <pascal.gloor at spale.com>
MFC after: 3 days