Prevent various redefined definitions in win32-specific code

From: Erik van Pienbroek <epienbro@fedoraproject.org>
Date: Mon, 22 Dec 2014 18:02:09 +0100
Revert "Fix: avoid assignment discards 'const' qualifier warning"

This reverts commit 0dbabcc44c141d0018a6eb6b6d3c78cc6e16491c.
Breaks other OpenSSL versions.