This is for adding a EGL-based renderer which is done via the ANGLE
project, which translate EGL calls to Direct3D 9/11.  This is done as a
possible solution to issue #105, especially for cases where the needed
full GL extensions to map OpenGL to Direc3D is unavailable or
unreliable, or when the OpenGL implementation from the graphics drivers
are problematic.

To enable this, do the following:
-Build ANGLE and ensure the ANGLE libEGL.dll and libGLESv2.dll are
 available.  A sufficiently-recent ANGLE is needed for things to
 work correctly--note that the copy of ANGLE that is included in
 qtbase-5.10.1 is sufficient.  ANGLE is licensed under a BSD 3-clause
 license.  Note also that Visual Studio 2013 or later is required to
 build ANGLE from QT-5.10.1, but the 2013-built ANGLE DLLs can work
 without without problems for GTK+ that is built with Visual Studio
 2008 or later.
-Build libepoxy on Windows with EGL support enabled.
-Define GDK_WIN32_ENABLE_EGL when build...