Make Wayland::EGL optional again
Review Request #126202 - Created Nov. 30, 2015 and submitted
This is needed to make KWin build-able on non-Linux, but is actually only a workaround. The dependency should also be available on non-Linux. This disables the EGL integration in the Wayland backend (QPainter still available) and the EGL fallback in the qpa plugin (preferred context sharing still available, but requires a working OpenGL Scene).
Only tried compiling with the dependency. Needs testing whether it works on the affected platforms.