kbuild: don't include `check-lxdialog' ldflags in global HOST_LOADLIBES

On BSD systems, `check-lxdialog' would select -lcurses as the default
curses library which would conflict with -lncurses at runtime: curses'
compatible symbols are getting handled by the system's curses library while the
ncurses-specific symbols are getting handled by the ports' ncurses.

This fixes `nconf' segmentation fault on these systems.

Signed-off-by: Arnaud Lacombe <lacombar@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>