build test, forward compatible context init

[Displacer]

build test option for cmake, query forward compatible context from freeglut (needed for mesa free drivers)

[Displacer]

skaslev, it would be nice if there are some comments on closing this issue and probably (wrong?) code in merge request.

[skaslev]

The CMake changes are fine.

The reason I didn't merge it is the additional GL/freeglut_ext.h header dependence. The test.c program is supposed to be built with any glut, not necessarily freeglut. Ideally test.c should be using a modern library that supports core profile creation out of the box such as glfw.

Sorry about ditching it all together without any comment.

[tombsar]

I was working on a minimal example using glfw some time ago. Would a PR for that be welcome?

[skaslev]

Absolutely.