Fix setting of SPICE_{GLIB,GTK}_REQUIRES
Fix setting of SPICE_{GLIB,GTK}_REQUIRES

Because of a typo (REQUIRED vs REQUIRES), these variables only
contained the last require that was set rather than a concatenation
of all the needed libraries.

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