Display required during build

[tnp0]

Since the changes to icons in 7.1, a GLX/opengl compatible "display" is required during the build process, making it very awkward to build for android on a headless server.

I've attempted to use xvfb, but it's opengl support isn't great I didn't have much luck in getting it running, in the end I relented and installed x11, and was able to build successfully.

Would it be possible to either fallback on an alternative to generate the icons (such as ffmpeg?), or add the ability to package manually created icons, there by skipping the need for icon generation entirely?

Cheers.