net-p2p/namecoin: fix for upcoming FORTIFY_SOURCE
On FreeBSD strlcat and strcpy exist so you should be using the
native libc versions instead of redefining your own.
FORTIFY_SOURCE depends on using the system headers so this change
fixes that case too.
PR: 202603
Submitted by: pfg, op
Approved by: milios@ccsys.com (maintainer)