bug#66175: Cannot create graphical frame using emacsclient -c when using pgtk

[Jonas Møller]

Hi, when using the old X11 GTK3 build of Emacs I was able to run emacs --daemon​, then create new graphical Emacs frames with emacsclient -c​.

Now-- with pgtk-- running emacsclient -c will always create a console frame. With the DISPLAY​ environment variable defined, it also produces a warning about using the pgtk build on X11.

I think the logic for deciding whether or not to start a graphical or terminal frame needs to be revisited with Wayland/pgtk in mind.

Also Wayland systems will still often define DISPLAY​, for compatibility with any legacy X11 apps that may need it. So checking for the existence of this env variable is not a sound strategy for deciding whether that warning about running on X11 should be emitted.