configure: suppress unused variable warnings if gst debugging is disabled
configure: suppress unused variable warnings if gst debugging is disabled

https://bugzilla.gnome.org/show_bug.cgi?id=662952

ensonic/gstreamer,surround-io/gstreamer,shelsonjava/gstreamer,cablelabs/gstreamer,cfoch/gstreamer,cablelabs/gstreamer,surround-io/gstreamer,surround-io/gstreamer,drothlis/gstreamer,lovebug356/gstreamer,ylatuya/gstreamer,StreamUtils/gstreamer,cablelabs/gstreamer,drothlis/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,lovebug356/gstreamer,lubosz/gstreamer,jpxiong/gstreamer,mparis/gstreamer,collects/gstreamer,krieger-od/gstreamer,jpakkane/gstreamer,ylatuya/gstreamer,justinjoy/gstreamer,centricular/gstreamer,mparis/gstreamer,drothlis/gstreamer,justinjoy/gstreamer,cfoch/gstreamer,collects/gstreamer,jpakkane/gstreamer,centricular/gstreamer,ensonic/gstreamer,krichter722/gstreamer,lovebug356/gstreamer,collects/gstreamer,Distrotech/gstreamer,collects/gstreamer,Distrotech/gstreamer,drothlis/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,lovebug356/gstreamer,jpxiong/gstreamer,Distrotech/gstreamer,Lachann/gstreamer,jpakkane/gstreamer,shelsonjava/gstreamer,jpxiong/gstreamer,lovebug356/gstreamer,ylatuya/gstreamer,cablelabs/gstreamer,krieger-od/gstreamer,krieger-od/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,ensonic/gstreamer,Lachann/gstreamer,Distrotech/gstreamer,ensonic/gstreamer,jpxiong/gstreamer,lubosz/gstreamer,centricular/gstreamer,collects/gstreamer,krieger-od/gstreamer,shelsonjava/gstreamer,lubosz/gstreamer,surround-io/gstreamer,jpakkane/gstreamer,justinjoy/gstreamer,StreamUtils/gstreamer,Lachann/gstreamer,shelsonjava/gstreamer,cablelabs/gstreamer,cfoch/gstreamer,drothlis/gstreamer,justinjoy/gstreamer,surround-io/gstreamer,justinjoy/gstreamer,centricular/gstreamer,cfoch/gstreamer,shelsonjava/gstreamer,ylatuya/gstreamer,Lachann/gstreamer,krieger-od/gstreamer,krichter722/gstreamer,ensonic/gstreamer,mparis/gstreamer,lubosz/gstreamer,Lachann/gstreamer,jpakkane/gstreamer,mparis/gstreamer,lubosz/gstreamer,Distrotech/gstreamer,krichter722/gstreamer,cfoch/gstreamer,ylatuya/gstreamer,centricular/gstreamer,mparis/gstreamer