Sereal's csnappy Win32 fixes

This commit contains fixes for MS Visual C on Win32 that were developed for
the Sereal serialization library at https://github.com/Sereal/Sereal .

Authors:

Steffen Mueller <smueller@cpan.org>
Yves Orton <yves.orton@booking.com>
bulk88 <bulk88@hotmail.com>