X11 Add support for video/screen scaling

[buserror]

On a 4K screen, GSport window is /tiny/ -- this PR adds support for scaling, by adding support for rendering via the XRender extension using a scaling transform. It should be accelerated on pretty much any hardware these days, so has no real impact on performance.

Technically this makes the scaling configurable at runtime, but at the moment it is #defined as x2. I tried to minimize impact on existing code.

This PR also contains a few little fixes for modern GCC, for example there is a commit to use __builtin_bswap; it also force align the prodos.h structures, as that wouldn't work on 64 bits systems at least using gcc.

[buserror]

Anyone knows if this project has been forked into something that accepts PRs? it's been nearly 3 years now...

[david-schmidt]

Hey, good to hear from you again! This one somehow escaped my notice. I'd say "we still accept PRs," but I see what you mean here. :-)

The upstream KEGS project is here, but Kent doesn't do GitHub, so contribution is a little more old-school: https://kegs.sourceforge.net/

I'm maintaining a GitHub-based mirror of it to make creating patches easier: https://github.com/david-schmidt/KEGS-upstream