Fix build error on WIN32 from _bpy.context_members

As of [0] which references context arrays from the Python API,
C++ name mangling caused 'node_context_dir' not to be found for WIN32.

[0]: c8edc458d1

source/blender/editors/space_node/node_intern.hh

@@ -31,7 +31,9 @@ struct wmKeyConfig;
 struct wmWindow;
 
 /* Outside of blender namespace to avoid Python documentation build error with `ctypes`. */
+extern "C" {
 extern const char *node_context_dir[];
+};
 
 namespace blender::ed::space_node {
 

source/blender/editors/space_node/space_node.cc

@@ -826,8 +826,10 @@ static void node_region_listener(const wmRegionListenerParams *params)
 }  // namespace blender::ed::space_node
 
 /* Outside of blender namespace to avoid Python documentation build error with `ctypes`. */
+extern "C" {
 const char *node_context_dir[] = {
     "selected_nodes", "active_node", "light", "material", "world", nullptr};
+};
 
 namespace blender::ed::space_node {