filesink: fix build on Cygwin
filesink: fix build on Cygwin

... where __fbufsize is not available

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