gst-launch: fix compiler warnings for SIGHUP handlers on windows
gst-launch: fix compiler warnings for SIGHUP handlers on windows

Fix unused variable/function compiler warnings on windows.
The SIGHUP handling is only available under unix.

https://bugzilla.gnome.org/show_bug.cgi?id=783661

StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer