Provide out own strlcpy() and strlcat() routines if necessary.

Provide out own strlcpy() and strlcat() routines if necessary.

We now depend on the *full* semantics of those routines, including the
return value being usable for truncation checks.

If we're building for a UN*X that has them, define pcap_strl{cpy,cat} to
be strl{cpy,cat}.

If we're building for Windows using MSVC, define pcap_strl{cpy,cat}, not
strl{cpy,cat}.

Otherwise, build our won versions of pcap_strl{cpy,cat} from BSD-derived
source code.