Use -lbsd for strlcat/strlcpy, if needed and available
On BSD systems, strlcat and strlcpy are included in the C library and
nothing special is needed. On Linux systems they are not, but libbsd may
be available to provide them. Use it if so.
This also adds wstrlcat and wstrlcpy instead of trying to maybe-provide
strlcat and strlcpy themselves, as that way there is no risk of symbol
conflicts. Not bumping the library version at this time, that should be
done (if necessary) before release.
Signed-off-by: Brad Jorsch <anomie@users.sourceforge.net>