Add -Wmissing-declarations -Wmissing-prototypes to configure flags
Add -Wmissing-declarations -Wmissing-prototypes to configure flags

And fix all warnings

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