bug#15094: Fix for posix_memalign on Cygwin

[Eli Zaretskii]

> Date: Wed, 14 Aug 2013 15:52:53 -0400
> From: Ken Brown <kbrown@cornell.edu>
> CC: 15094@debbugs.gnu.org
> 
> /* Cygwin allows applications to provide their own malloc.  As of
> cygwin-1.7.24, applications that provide their own malloc are also
> allowed to provide their own posix_memalign (but not memalign).  Calls
> to memalign are handled by Cygwin's memalign, which always returns
> ENOSYS if the application has defined its own malloc.  So we have to
> rename memalign in order to make sure that posix_memalign calls
> Emacs's memalign rather than Cygwin's.  */

How does Cygwin memalign come into play, when Emacs provides its own?