configure: disable opengl per default

There is a bug in nvidia's binary GPU driver, which causes a segmentation
fault if linked to libGL.
Signed-off-by: NMichael Walle <michael@walle.cc>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

configure

@@ -177,6 +177,7 @@ spice=""
 rbd=""
 smartcard=""
 smartcard_nss=""
+opengl="no"
 
 # parse CC options first
 for opt do