MSSDK61 in windows-amd64 build

[Max (Weijun) Wang]

Hi Kelly

This is the first time I build windows-amd64 with Visual Studio 2008.

At the freetypecheck stage, it cannot find the MSSDK61 path. According  
to make/common/shared/Defs-windows.gmk, it's something like --

    $(_program_files)/Microsoft SDKs/Windows/v6.1/

but on my system there's only C:\Program Files\Microsoft SDKs\Windows 
\v6.0A, and there's a WINDOWSSDKDIR env variable pointing to it.

Is version 6.1 a must? I've manually point MSSDK61 to $WINDOWSSSDKDIR  
and the build is running now.

Thanks
Max