configure: Add HAX support in NetBSD

The NetBSD support in Intel HAXM has beem merged upstream and is functional.
Signed-off-by: NKamil Rytarowski <n54@gmx.com>
Message-Id: <20190207233704.29978-1-n54@gmx.com>
Signed-off-by: NLaurent Vivier <laurent@vivier.eu>

configure

@@ -817,6 +817,7 @@ DragonFly)
 ;;
 NetBSD)
   bsd="yes"
+  hax="yes"
   make="${MAKE-gmake}"
   audio_drv_list="oss try-sdl"
   audio_possible_drivers="oss sdl"