build: also suppress unused-function warnings about g_autoptr

build: also suppress unused-function warnings about g_autoptr

../plugins/ges/gesdemux.c:50:1: error: unused function 'glib_autoptr_cleanup_GESDemux' [-Werror,-Wunused-function]
G_DECLARE_FINAL_TYPE (GESDemux, ges_demux, GES, DEMUX, GESBaseBin);
^
/home/matt/Projects/cerbero/build/dist/android_universal/x86_64/include/glib-2.0/gobject/gtype.h:1401:3: note: expanded from macro 'G_DECLARE_FINAL_TYPE'
  _GLIB_DEFINE_AUTOPTR_CHAINUP (ModuleObjName, ParentName)                                               \
  ^
/home/matt/Projects/cerbero/build/dist/android_universal/x86_64/include/glib-2.0/glib/gmacros.h:451:22: note: expanded from macro '_GLIB_DEFINE_AUTOPTR_CHAINUP'
  static inline void _GLIB_AUTOPTR_FUNC_NAME(ModuleObjName) (ModuleObjName **_ptr) {                     \
                     ^
/home/matt/Projects/cerbero/build/dist/android_universal/x86_64/include/glib-2.0/glib/gmacros.h:441:43: note: expanded from macro '_GLIB_AUTOPTR_FUNC_NAME'
#define _GLIB_AUTOPTR_FUNC_NAME(TypeName) glib_autoptr_cleanup_##TypeName
                                          ^
<scratch space>:81:1: note: expanded from here
glib_autoptr_cleanup_GESDemux
^

../plugins/ges/gessrc.c:56:1: error: unused function 'glib_autoptr_cleanup_GESSrc' [-Werror,-Wunused-function]
G_DECLARE_FINAL_TYPE (GESSrc, ges_src, GES, SRC, GESBaseBin);
^
/home/matt/Projects/cerbero/build/dist/android_universal/x86_64/include/glib-2.0/gobject/gtype.h:1401:3: note: expanded from macro 'G_DECLARE_FINAL_TYPE'
  _GLIB_DEFINE_AUTOPTR_CHAINUP (ModuleObjName, ParentName)                                               \
  ^
/home/matt/Projects/cerbero/build/dist/android_universal/x86_64/include/glib-2.0/glib/gmacros.h:451:22: note: expanded from macro '_GLIB_DEFINE_AUTOPTR_CHAINUP'
  static inline void _GLIB_AUTOPTR_FUNC_NAME(ModuleObjName) (ModuleObjName **_ptr) {                     \
                     ^
/home/matt/Projects/cerbero/build/dist/android_universal/x86_64/include/glib-2.0/glib/gmacros.h:441:43: note: expanded from macro '_GLIB_AUTOPTR_FUNC_NAME'
#define _GLIB_AUTOPTR_FUNC_NAME(TypeName) glib_autoptr_cleanup_##TypeName
                                          ^
<scratch space>:158:1: note: expanded from here
glib_autoptr_cleanup_GESSrc
^