Using OpenGL Core Profile for x86 Generic build

It was not possible to build OpenGL without X11. I'm not sure if anything changed now.

Also, current Kodi master does not support HDR passthrough with OpenGL.

Quote from KOPRajs

I would like to ask, what is the motivation to use OpenGL ES instead of the Core Profile for main Generic x86 build.

Our smaller devices only support OpenGL ES. That means, those calls go directly to GPU (hardware accelerated).

OpenGL Core Profile for x86 would add another branch of development, which doesn't make sense for our needs (though it would make sense for yours).

LE's installed base is roughly 80% RPi boards, 10% x86_64 hardware, and 10% other ARM boards. The x86_64 devices break down as 70% Intel, 20% AMD, 10% nVidia; most of the nVidia cards are older ones requiring VDPAU and legacy drivers, not newer ones with NVDEC. LE users mostly run Kodi to watch videos, so features like HDR playback trump shader support for games. The legacy image exists to service a handful of nVidia users and those who require a browser to access certain streams. I'm not aware that you can build mesa with OpenGL without X11, which means no HDR, and the long term goal is to bin X11 and only support GBM, and with either a GBM 'browser' or worst-case Wayland, which supports HDR, but doesn't currently support refresh rate switching which is a must-have feature for Kodi movie viewers. So right now all roads point in the direction of ```GBM/OpenGLES, not OpenGL. If it's now possible to run a GBM/OpenGL environment that would be interesting, but we'll look into that direction once there's a complelling reason; e.g. Kodi finally has Retroplayer OpenGL capabilities. It doesn't make sense for us to switch from a known/good formula unless there's demand. If you've already built Generic/OpenGL/GBM images that work? we'd have no issue with the changes being submitted to make development easier; similar to how we have options for Generic/Wayland although we don't currently build it. There's also no issue to add changes in LE that reduce downstream technical debt in Lakka, if that's at-all a related objective.

My initial testing of OpenGL GBM x86 image looks good.

I PR'd a Kodi fix for HDR passthrough on OpenGL. Hopefully, it would be merged at some point.

That's interesting, although from a release management perspective I would not consider switching Generic to OpenGL for LE13 for two reasons:

a) It's getting close to the likely release schedule for K22 and this is slightly exotic and thus needs proper testing on a wide range of GPU hardware (and Generic users often have older hardware).

b) It's a breaking change for Kodi binary add-ons and I'd like a release without breaking changes. In the last two releases we did Python2>3 and arm>aarch64. This time around it's stable, but we'll get enough whinging from dropping nVidia 340.108 support.

There's no issue to add another build option earlier though.