gplugin/gplugin

Fix an issue where meson would fail if building without gtk3 support

2021-04-28, Gary Kramlich
b7c659d32d7a
Fix an issue where meson would fail if building without gtk3 support

Testing Done:
Ran `meson` (with no options) and verified that `ninja doc` built both `gplugin-doc` and `gplugin-gtk-doc`.

Ran `meson -Dgtk3=false` and verified that `ninja doc` just built `gplugin-doc`

Reviewed at https://reviews.imfreedom.org/r/629/
gplugin_query = executable('gplugin-query',
'gplugin-query.c',
dependencies : [gplugin_dep, GLIB, GOBJECT],
install : get_option('install-gplugin-query'))
if get_option('help2man')
custom_target('gplugin-query.1',
command : [help2man,
'--name=Query installed plugins', '--section=1',
'--help-option=--help-all', '--no-info',
'--output', '@OUTPUT@',
gplugin_query],
output : 'gplugin-query.1',
install : get_option('install-gplugin-query'),
install_dir : get_option('mandir') / 'man1')
endif