CMake: prepare for BLENDER_SORTED_LIBS removal

No functional change, this adds LIB definition and args to cmake files.
Without this it's difficult to migrate away from 'BLENDER_SORTED_LIBS'
since there are many platforms/configurations that could break when
changing linking order.

Manually add and enable WITHOUT_SORTED_LIBS to try building
without sorted libs (currently fails since all variables are empty).
This check will eventually be removed.

See T46725.

extern/xdnd/CMakeLists.txt

@@ -31,8 +31,11 @@ set(SRC
 	xdnd.h
 )
 
+set(LIB
+)
+
 add_definitions(
 	-DHAVE_SYS_TIME_H
 )
 
-blender_add_lib(extern_xdnd "${SRC}" "${INC}" "${INC_SYS}")
+blender_add_lib(extern_xdnd "${SRC}" "${INC}" "${INC_SYS}" "${LIB}")