Generate a dummy pc file for graphene-gobject
Generate a dummy pc file for graphene-gobject

The graphene-gobject pkg-config file should only list the required
dependencies, as it doesn't really have any additional compiler and
linker flags.

Aside from simplifying the build, it also removes a warning from Meson
telling us that we're build two pkg-config files for the same build
target.

ebassi/graphene,ebassi/graphene