Actually, pkgConfig path are a single string, for one file. Some people uses spaces as delimiter for multiple files. But it causes some issues on some OSes (like Arch Linux), because it does not split correctly names.
The main example is SwiftGtk that is unbuildable on arch linux because of GLib's pkg-config files (glib-2.0 and gio-unix-2.0) are recognized diffently on Ubuntu by example ("glib-2.0.pc" and "gio-unix-2.0.pc") and Arch-derrivatives ('glib-2.0 gio-unix-2.0.pc').
Possible fix: use pkgConfig: [String] with an array to let developer properly split its pkg-config files.