dev-libs/liboil-0.3.12 always depends on glib for building. Even without glib present, the library builds fine. According to the liboil website [1]: "GLib-2.0 is recommended to build a few of the examples, but is not required for anything that is installed." IMHO this means that the dependency can simply be removed. Alternatively, if there is some added value of having glib, please protect the dependency by a glib useflag. This allows the use of liboil on embedded gentoo, where glib is not available. [1]: http://liboil.freedesktop.org/wiki/
Please make it dependendent on the "examples" use flag then. Makes a lot more sense.
Reassigning to maintainer-needed since zaheerm has left Gentoo, bug #68473.
I thought it would be as easy as removing examples folder from the Makefiles but it's a bit more complicated than that (as usual). liboil provides an utility for oid bugreport but it is in examples folders. Some other programs might be of interest too but for now I think I'll just keep this one and will commit a fix soonish.
Fixed in 0.3.15-r1. Thanks for the report and please reopen if it's still not fixed for you.