QtWebEngine fails to build when configured with -no-opengl

This is a problem exclusive to dev (5.8 and greater) since it became possible to build QtDeclarative without OpenGL (via the software renderer).

So what happens is when you build Qt and then QtWebengine, it is possible for all the tests to pass because it checks the system libKHR not if Qt has OpenGL support.

So the build will fail when it tries to use non-existing classes like QOpenGLContext.

But... It should actually be possible to build an run a use-able version of QtWebEngine with a QT_NO_OPENGL build of Qt 5.8 because the Qt Quick 2D Renderer is now part of QtDeclarative. Previously it was possible to run QtWebEngine on systems without OpenGL (via the use of a OpenGL headers + a fake stub lib), which meant that even those the code that was built included and linked against OpenGL API's in Qt like QOpenGLContext, it manages to run without calling any of those API's, because if they did, the application would have crashed.

So I propose that this bug should not be addressed as "not supported anyway" and a one line:

contains(QT_CONFIG, opengl):

But rather enable QtWebEngine to be built without support for OpenGL, but still use the same Scenegraph API's to render web content.