f17 and rawhide have pkg-config 0.25. The 0.26 version was released last May and fixes one bug that we just hit when trying to build gnome-boxes: - Fix up pkg.m4 to handle the case of --exists working and --cflags or --libs failing. Due to a bug in the spice-gtk package (caused by an rpm bug), the requires for the packages required in spice-gtk .pc files were not automatically added to the spice-gtk development package. This caused the spice-gtk .pc files to require non-existing .pc files, which means pkg-config --exists worked, but pkg-config --cflags --libs failed. Due to the pkg.m4 bug mentioned above, this error didn't appear in the build log, which made things harder to diagnose.
pkg-config 0.26 has been pushed to rawhide.