after setting set CPATH=C:\WpdPack\IncludeWell that, at least, is working - the WpdPack headers are now being found. (Btw, if you ever need to, you can set CPATH to multiple directories by separating them with a ';' same as for the PATH variable.)
If you can contact the Net::Pcap developers and tell them of these errors, they might be able to help.
It looks to me that stubs.inc is in need of some alterations. I would think that the warnings are nothing to worry about, but the 'conflicting types' and 'redefinition' errors are definite showstoppers.
I would go through stubs.inc and comment out (or remove) the code that's giving rise to these errors, but I couldn't guarantee that's the correct approach and I'm not in a position to try it out for myself.
Then, when stubs.inc has been fixed, build the module manually (ie not using cpan) as already detailed.
It looks like this bug (or something very similar) in the Net::Pcap source
has already been reported about nine months ago .... getting assistance from the developer(s) is looking a bit unlikely. If you do try amending stubs.inc, and it works, you might like to update that bug report with the solution.
Cheers,
Rob