build: fix --disable-gl if cuda is enabled

video/out/opengl/hwdec_cuda.c is enabled with cuda-hwaccel. But it makes
only sense to build if GL is enabled, and in fact it fails to link
without GL as it calls a specific GL helper function.

In theory it would be perfectly possible to use cuda-copy with GL
disabled. But I'm not bothering with the complexity.

wscript

@@ -850,6 +850,7 @@ hwaccel_features = [
     }, {
         'name': '--cuda-hwaccel',
         'desc': 'CUDA hwaccel',
+        'deps': [ 'gl' ],
         'func': check_cc(fragment=load_fragment('cuda.c'),
                          use='libav'),
     }, {