This is required at build time as the `gplugin-native-plugin.h` header includes GModule headers, and must be passed to anything using GPlugin as a subproject.
Testing Done:
Compiled without GModule on standard include path.
Reviewed at https://reviews.imfreedom.org/r/2642/
ifnotget_option('install-gplugin-gtk4-viewer')
summary('gplugin-gtk4-viewer',
'You have disabled installation of gplugin-gtk4-viewer which is a '+