nvcodec: Stop building for non-{Windows,Linux} target

The other platforms, specifically macOS have not been supported already
because this plugin loads so or dll. Moreover, NVIDIA dropped
support for macOS as of CUDA 11.0. See also
https://developer.nvidia.com/nvidia-cuda-toolkit-11_0_0-developer-tools-mac-hosts

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2283>

subprojects/gst-plugins-bad/gst-libs/gst/cuda/meson.build

@@ -20,6 +20,12 @@ cuda_headers = [
     'gstnvrtcloader.h',
 ]
 
+gstcuda_dep = dependency('', required : false)
+
+if host_system not in ['windows', 'linux']
+  subdir_done()
+endif
+
 cuda_stubinc = include_directories('./stub')
 extra_c_args = ['-DGST_USE_UNSTABLE_API']
 

subprojects/gst-plugins-bad/sys/nvcodec/meson.build

@@ -31,6 +31,13 @@ if get_option('nvcodec').disabled()
   subdir_done()
 endif
 
+if not gstcuda_dep.found()
+  if get_option('nvcodec').enabled()
+    error('The nvcodec was enabled explicitly, but required gstcuda dependency is not found')
+  endif
+  subdir_done()
+endif
+
 plugin_incdirs = [configinc, cuda_stubinc]
 extra_args = ['-DGST_USE_UNSTABLE_API']