[PATCH] xdiff: fix trivial build warnings on Windows

[Jun Wu]

Excerpts from Yuya Nishihara's message of 2018-03-08 21:33:42 +0900:
> On Tue, 6 Mar 2018 19:12:26 -0800, Jun Wu wrote:
> > Yeah, xdiff needs a migration from using "long", "int"s to "size_t" etc.
> > The git community has chosen to disallow diff >1GB files because of the
> > overflow concern [1].
> > 
> > [1]: https://github.com/git/git/commit/dcd1742e56ebb944c4ff62346da4548e1e3be675
> 
> So, should we queue this now or leave warnings to denote things that should
> be cleaned up?

I think the ideal solution would be replacing all "long"s to one of:
"int64_t" or "ssize_t", "size_t", instead of doing casting around.

I can talk a look at the actual change, since I think I have some knowledge
about xdiff internals now.