Why the heck does ftp.gnome.org host (apparently two strains of) pkg-config?
http://ftp.gnome.org/pub/GNOME/sources/pkg-config/ (version 0.18 and 0.19)
http://ftp.gnome.org/pub/GNOME/sources/pkgconfig/ (version 0.8 through 0.18, though skipping 0.10)
It’s irresponsible to host out-of-date versions like that, as if pkg-config was part of the Gnome project and didn’t exist independently. At least put a README or something which mentions that this is a possibly-out-of-date mirror!
The real pkg-config distribution is here:
with releases (including the current 0.23) here: