build-sys: fix --with-sasl
build-sys: fix --with-sasl

The default configure sasl auto setting will error out if SASL is
missing. Instead, silentely skip sasl configure if detected missing.

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