Runtime switching between desktop OpenGL and OpenGL ES not supported

We'd like to select whether to use OpenGL ES or desktop OpenGL, but currently that's limited to a one-time build option. It'd be preferred if it would be made into a runtime option instead, so as not to need the whole stack twice.

We're currently setting -opengl es2 on ARM architectures and -opengl desktop on x86. But we'd need OpenGL ES instead for an emulator also on x86 and in case it's required/preferred on some hardware/drivers, while desktop OpenGL is obviously better on some other hardware and used by some Qt projects (KDE for example uses OpenGL 3.0 features when available).

The Qt 5.2.1 enabled compiling EGL support together with desktop OpenGL, which is a good step but essentially all combinations EGL/GLX/OpenGL/OpenGLES would need to be runtime selectable to cover all use cases.