gplugin/gplugin

Fix some issues with the gtk3 and gtk4 includes when not used in a subproject

23 months ago, Gary Kramlich
5362a1727bf6
Fix some issues with the gtk3 and gtk4 includes when not used in a subproject

Testing Done:
Ran the unit tests and gplugin-gtk4-viewer and verified no issues.

Bugs closed: GPLUGIN-145

Reviewed at https://reviews.imfreedom.org/r/1469/
The following individuals have contributed to this project.
Ankit Vani <a@nevitus.org>
EionRobb <eion@robbmob.com>
Elliott Sales de Andrade <quantum.analyst@gmail.com>
Gary Kramlich <grim@reaperworld.com>
Jason Scherer <schereja@gmail.com>
John Bailey <rekkanoryo@rekkanoryo.org>
Mike Ruprecht <cmaiku@gmail.com>
Olaf Hering <olaf@aepfle.de>
Paul Jimenez <pj@place.org>
Richard Laager <rlaager@pidgin.im>
Sorvival <sorvival@tutanota.com>
ivanhoe <ivanhoe@fiscari.de>