[Box Backup-dev] makebuildenv.pl and Win32

[Ben Summers]

I'd like this statement

    $env_flags{'IGNORE_lib/win32'} = 1;

to be executed at around line 40 of makebuildenv.pl if and only if  
the platform is Win32. What's the autoconf way of doing this?

The idea is to stop the win32 directory from being included,  
compiled, or anything, unless we're on win32.

Ben