PING [4.1 regression, patch] build i686-pc-mingw32

[Paolo Bonzini]

>Paolo, could you go back and think about the bootstrapping problem
>from MinGW's perspective?
>  
>
I had considered cygwin, that had some problems because of the 
executable-file extension.  I had also thought of using batch files via 
config.build, but got stuck because Windows. does not have as far as I 
know, the equivalent of "$@"; and anyway it seems strange to need a 
batch file where everything else is msys-based.  So yes, I think the 
solution of hacking pex-win32.c is great.

Paolo