How to build FTEQCCGUI on Arch Linux?

[NHogweed]

make gtkgui in engine\qclib fails due to qcc_gtk.c missing. Should qccguiqt.cpp be used instead? If so, Makefile needs to be updated.

[hemebond]

Not sure about Arch, but for Debian:

1. Install qscintilla and qt5widgets dev packages
2. cmake .
3. make fteqccgui

@eukara Would it be possible to add fteqccgui for Linux to the build pipelines?

[Jaypers]

Having a compiled Linux version would be really nice (especially for a noob like me)