[Users] claws-mail impap-error Port 993 tls on Macos

[David Fletcher]

I see the problem now:
https://docs.gtk.org/gtk3/class.Socket.html

"The GtkPlug and GtkSocket widgets are only available when GTK+ is
compiled for the X11 platform and GDK_WINDOWING_X11 is defined. They can
only be used on a GdkX11Display. To use GtkPlug and GtkSocket, you need
to include the gtk/gtkx.h header."

So it's not just about GDK_WINDOWING_X11 define statements cutting out
headers, the underlying use of GtkSocket won't work in the Mac with the
Quartz backend to GTK.