Fix compile-time warnings on all perl code

Fix compile-time warnings on all perl code

This patch does two things. First, it silences a number of compile-time
warnings in the msvc tools files, mainly those due to the fact that in
some cases we have more than one package per file. Second it supplies a
dummy Perl library with just enough of the Windows API referred to in
our code to let it run these checks cleanly, even on Unix machines where
the code is never supposed to run. The dummy library should only be used
for that purpose, as its README notes.