package/x11r7/xlib_libXfont2: fix usage of libbsd

package/x11r7/xlib_libXfont2: fix usage of libbsd

Upstream added optional support for libbsd:
"Add strlcat & strlcpy fallbacks if not provided by libc nor libbsd"
https://cgit.freedesktop.org/xorg/lib/libXfont/commit/?id=d4c941ea8b1dc07a14efce656bff58d31a14c985

and forgot to define HAVE_LIBBSD.

Also add libbsd as optional dependency because the build error occured
only when libbsd was built before building xlib_libXfont2.

Fixes:
http://autobuild.buildroot.net/results/165/165f9f948419fc69fbf6b9281d759b37bb7d40c6/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>