package/lynx: add dependency on host-pkgconf

package/lynx: add dependency on host-pkgconf

The Lynx configure script uses pkg-config when available:

checking for nios2-buildroot-linux-gnu-pkg-config... /home/thomas/projets/buildroot/output/host/bin/pkg-config
checking pkg-config for openssl... yes
[...]
checking pkg-config for ncurses... yes

Using pkg-config avoids build failures such as:

checking for _nc_freeall... no
configure: error: Configuration does not support color-styles
make: *** [/home/test/autobuild/run/instance-1/output/build/lynx-2.8.9rel.1/.stamp_configured] Error 1

When building with "make lynx", so that pkg-config is not built
before. The issue is that in this case, lynx configure script picks up
the ncurses6-config script for the host ncurses instead of the one in
staging. Using pkg-config solves that nicely.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>