filesink: Fix fsync/_commit usage
filesink: Fix fsync/_commit usage

_MSC_VER will only be defined when building *on* windows and not just
*for* windows. Instead, use the G_OS_WIN32 define

StreamUtils/gstreamer,jpxiong/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,shelsonjava/gstreamer,shelsonjava/gstreamer,jpxiong/gstreamer,centricular/gstreamer,centricular/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,krichter722/gstreamer,krichter722/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,krichter722/gstreamer,jpxiong/gstreamer,shelsonjava/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,jpxiong/gstreamer