[PATCH] Update build procedure in setup README

[Dave Korn]

Eric Blake wrote:
> According to Dave Korn on 7/22/2009 2:34 PM:
>>   Makes sense to everyone?  (CC_FOR_BUILD defaults to just 'cc' if you don't
>> set it; it's utterly non-critical which version of GCC is used, however, so I
>> didn't bother to add a version suffix to that one.)
> 
>> +       --build=i686-pc-cygwin CC="gcc-3 -mno-cygwin" CXX="g++-3 -mno-cygwin" \
> 
> gcc-3, or gcc-4?

  gcc-4 doesn't support -mno-cygwin, so it has to be gcc-3.  When there's an
i686-pc-mingw32-gcc-4, we can update it again...

    cheers,
      DaveK