pkgconf: new package

pkgconf is a drop-in replacement for pkg-config that doesn't need
itself to build and just requires a C89 compiler.

Instead of using a patch for hardcoded sysroot support (as the patch to
pkg-config does) we rely instead on a wrapper script that takes the
appropiate action.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>