editor: add a Gtk4 port

2 jobs for lr/gtk-4.0 in 2 minutes and 53 seconds (queued for 5 seconds)
Status Name Job ID Coverage
  Build
failed fedora28_dist #1600415

00:02:53

 
  Test
skipped fedora_from_dist #1600416
 
Name Stage Failure
failed
fedora28_dist Build
Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.

Alternatively, you may set the environment variables GTK4_CFLAGS
and GTK4_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.
make: *** [Makefile:1647: distcheck] Error 1
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1