buildsys: Disable some warnings
buildsys: Disable some warnings

Mostly so that they don't turn into errors when building from source:
-Wno-missing-field-initializers:
Because this has to be close to the most stupid warning gcc has ever produced
-Wno-deprecated-declarations
Because we use some deprecated functions to avoid #ifdef hell while maintaining
compat with older gtk / glib versions

Signed-off-by: Hans de Goede <9fa1be1a5b5729e4c6b404f34c9ce49ff4882fd8@redhat.com>

mathslinux/spice-gtk,SPICE/spice-gtk,Fantu/spice-gtk,fgouget/spice-gtk,elmarco/spice-gtk,dezelin/spice-gtk,mathslinux/spice-gtk,fgouget/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,fgouget/spice-gtk,mathslinux/spice-gtk,guodong/spice-gtk,Fantu/spice-gtk,SPICE/spice-gtk,elmarco/spice-gtk,SPICE/spice-gtk,dezelin/spice-gtk,mathslinux/spice-gtk,Fantu/spice-gtk,Fantu/spice-gtk,dezelin/spice-gtk,flexVDI/spice-gtk,flexVDI/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,SPICE/spice-gtk,dezelin/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,guodong/spice-gtk,elmarco/spice-gtk,guodong/spice-gtk,elmarco/spice-gtk,guodong/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk