Backported from X.org:

commit 1324b0ca9f8a7fdaf03b374c75eb3c9df407c2f1
Author: Colin Harrison <colin.harrison@virgin.net>
Date:   Fri Dec 10 00:08:24 2010 +0000

    Typo in xserver Xvasprintf()

    I needed this patch in the wrapper around vsnprintf() in os/xprintf.c
    (MinGW for Windows build) to correct various crashes.
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Backported-to-NX-by: Mihai Moldovan <ionic@ionic.de>