Remove the restriction of detecing QtOpenGL module just when the gl.h header was found.
Remove the restriction of detecing QtOpenGL module just when the gl.h header was found.

This is needed to be able to compile the QtOpenGL module on Linux when using OpenGL-ES
backend. On the other hand OpenGL-ES support isn't yet supported under MS Windows but I
don't think that this should be a problem at all.

BadSingleton/pyside2,enthought/pyside,M4rtinK/pyside-android,BadSingleton/pyside2,RobinD42/pyside,PySide/PySide,M4rtinK/pyside-android,pankajp/pyside,pankajp/pyside,M4rtinK/pyside-android,IronManMark20/pyside2,M4rtinK/pyside-bb10,IronManMark20/pyside2,M4rtinK/pyside-android,qtproject/pyside-pyside,M4rtinK/pyside-bb10,M4rtinK/pyside-android,M4rtinK/pyside-bb10,M4rtinK/pyside-bb10,enthought/pyside,enthought/pyside,gbaty/pyside2,IronManMark20/pyside2,RobinD42/pyside,BadSingleton/pyside2,gbaty/pyside2,enthought/pyside,enthought/pyside,RobinD42/pyside,M4rtinK/pyside-android,gbaty/pyside2,PySide/PySide,qtproject/pyside-pyside,enthought/pyside,pankajp/pyside,PySide/PySide,BadSingleton/pyside2,PySide/PySide,IronManMark20/pyside2,enthought/pyside,qtproject/pyside-pyside,RobinD42/pyside,qtproject/pyside-pyside,RobinD42/pyside,qtproject/pyside-pyside,gbaty/pyside2,gbaty/pyside2,RobinD42/pyside,PySide/PySide,pankajp/pyside,M4rtinK/pyside-bb10,pankajp/pyside,BadSingleton/pyside2,M4rtinK/pyside-bb10,RobinD42/pyside,IronManMark20/pyside2