udftools: fix static linking against readline

One program of udftools uses the readline library, but fails to build
in static linking configurations. In order to fix this, we teach
udftools configure.ac to use pkg-config to detect the readline
library, and to use the proper flags provided by pkg-config.

This obviously requires an autoreconf of the package, and the addition
of host-pkgconf in the dependencies.

Fixes:

  http://autobuild.buildroot.net/results/113a94049d89b8f065112e5d4482667a7b7fb843/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>