gplugin/gplugin

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/
if get_option('gtk3')
if not get_option('install-gplugin-gtk3-viewer')
summary('gplugin-gtk3-viewer',
'You have disabled installation of gplugin-gtk-viewer which is a ' +
'very useful diagnostics tool.',
section : 'Warnings')
endif
gplugin_gtk3_viewer_resources = gnome.compile_resources(
'gplugin-gtk-viewer-resources',
'data/gplugin-gtk-viewer.gresource.xml',
c_name: 'gplugin_gtk_viewer',
source_dir: 'data')
gplugin_gtk3_viewer = executable('gplugin-gtk3-viewer',
'gplugin-gtk-viewer.c',
'gplugin-gtk-viewer-window.c',
'gplugin-gtk-viewer-window.h',
dependencies : [gplugin_dep, gplugin_gtk3_dep],
install : get_option('install-gplugin-gtk3-viewer')
)
if get_option('help2man')
gplugin_gtk_viewer_man = custom_target('gplugin-gtk3-viewer.1',
command : [help2man,
'--name=View installed plugins', '--section=1',
'--help-option=--help-all', '--no-info',
'--output', '@OUTPUT@',
gplugin_gtk3_viewer],
output : 'gplugin-gtk3-viewer.1',
install : get_option('install-gplugin-gtk3-viewer'),
install_dir : get_option('mandir') / 'man1')
endif
endif