Failing to build QtGStreamer elements on Windows

[Josh Doe]

I'm trying to build the QtGStreamer plugin (gstqt5videosink) for
x86_64 using Visual Studio 2012, GStreamer 1.4.1, Qt 5.2.1, and
qt-gstreamer HEAD.

I first had to update the CMake modules to use the
GSTREAMER_1_0_ROOT_X86_64 env var since I didn't have pkg-config. I
then had to change the usage of the MSVC "interface" keyword in
GstQtGLVideoSinkBase::colorbalance_init. After this I could compile,
but then linking fails.

Linking fails with unresolved external symbol __imp_glActiveTexture
referenced in VideoMaterial::bind(void). All other GL symbols seem to
resolve okay.

If I disable GL, the other elements build fine and seem to work well.
Unfortunately now I'm trying to work a 4k video source and
qwidget5videosink is too slow.

Thanks,
-Josh