If windowsdriproto headers are available, build a Windows-DRI extension,
which supports requests to enable local clients to directly render GL to a
Windows drawable:

- a query to check if WGL is being used on a screen
- a query to map a fbconfigID to a native pixelformatindex
- a query to map a drawable to a native handle

Windows-DRI can only be useful if we are using WGL, so make an note if WGL
is active on a screen.

Make validGlxDrawable() public

Adjust glxWinSetPixelFormat() so it doesn't require a context, just a
screen and config.

That enables factoring out the deferred drawable creation code as
glxWinDeferredCreateDrawable()

Enhance glxWinDeferredCreateDrawable(), so that pixmaps are placed into a
file mapping, so they exist in memory which can be shared with the direct
rendering process.

Currently, this file mapping is accessed by a name generated from the XID.
This will not be unique across multiple server instances. It would perhaps
be better, although more complicated, to use an anonymous file mapping, and
then duplicate the handle for the direct rendering process.

Use glxWinDeferredCreateDrawable() to ensure the native handle exists for
the Windows-DRI query to map a drawable to native handle.

v2:
Various printf format warning fixes

v3:
Fix format warnings on x86
Move some uninteresting windows-dri output to debug log level

v4:
check for windowsdriproto when  --enable-windowsdri
use windowsdriproto_CFLAGS

Signed-off-by: Jon Turney <jon.turney@dronecode.org.uk>
Reviewed-by: Colin Harrison <colin.harrison@virgin.net>