libfribidi: depend on host-pkgconf

libfribidi needs macros from pkgconf to generate its configure script. Since
commit 5693f236 (libfribidi: bump version) we AUTORECONF, so host-pkgconf
is also needed.

Fixes:
http://autobuild.buildroot.net/results/5d7/5d76a8333fb05e903460ad51dc0737c18431d033/



Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>