Add a HISTORY section for memcpy(3) and mempcpy(3)

The memcpy() function first appeared in AT&T System V UNIX and was
reimplemented for 4.3BSD-Tahoe. The mempcpy() function first appeared in
FreeBSD 13.1.

PR: 272227
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D42630