Windows PTP support not integrated into build system

See https://gitlab.freedesktop.org/gstreamer/gstreamer/-/blob/main/subprojects/gstreamer/libs/gst/helpers/meson.build#L30-31

elif host_system == 'windows'
  message('PTP not supported on Windows, not ported yet.')

The PTP code contains Windows-specific code paths so I assume this was working with the autotools build.

CC @nirbheek