deps/libff: Don't build libff (deprecated)

deps/CMakeLists.txt

@@ -5,7 +5,11 @@ endif()
 
 add_subdirectory(glad)
 add_subdirectory(ipc-util)
-add_subdirectory(libff)
+
+if(BUILD_LIBFF)
+	add_subdirectory(libff)
+endif()
+
 add_subdirectory(media-playback)
 add_subdirectory(file-updater)