codegen: ifdef/endif function declaration too
codegen: ifdef/endif function declaration too

Compile out part that we are not supporting.  In the future, we might
want to declare a fake type and an empty function to keep API
compatibility

fgouget/spice-common,Fantu/spice-common,SPICE/spice-common,fgouget/spice-common,SPICE/spice-common,SPICE/spice-common,freedesktop-unofficial-mirror/spice__spice-common,elmarco/spice-common,Fantu/spice-common,fgouget/spice-common,elmarco/spice-common,elmarco/spice-common,elmarco/spice-common,freedesktop-unofficial-mirror/spice__spice-common,Fantu/spice-common,freedesktop-unofficial-mirror/spice__spice-common,freedesktop-unofficial-mirror/spice__spice-common,Fantu/spice-common,fgouget/spice-common