Add header with structure sizes for 64-bit windows as well.
They're almost the same as on Linux, but it looks like things
like padding unions get aligned slightly differently so there
are a handful of differences:

 sizeof(GstGhostPad) is 528, expected 536
 sizeof(GstPad) is 512, expected 520
 sizeof(GstPadProbeInfo) is 64, expected 72
 sizeof(GstProxyPad) is 520, expected 528