First, the current patch doesn't apply cleanly to trunk. The following
patch should be ok (some of the changes of the original patch apparently
have been committed separately in the meantime).

Second, the patch allows me to do a 32-bit build (under 64-bit Linux) by
doing:
  CFLAGS=-m32 LDFLAGS=-m32 ./configure
rather than:
  CC="gcc -m32" ./configure
However, if I omit LDFLAGS it doesn't work, I don't know if it's intended.

Third, while the 32-bit build does work, the shared objects are still
placed in a directory called "lib.linux-x86_64-2.7", which I suppose is
wrong:

$ ./python
Python 2.7a0 (trunk:75966:75967M, Oct 30 2009, 22:55:18) 
[GCC 4.3.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import _socket
>>> _socket.__file__
'/home/antoine/cpython/__svn__/build/lib.linux-x86_64-2.7/_socket.so'

$ file /home/antoine/cpython/__svn__/build/lib.linux-x86_64-2.7/_socket.so
/home/antoine/cpython/__svn__/build/lib.linux-x86_64-2.7/_socket.so: ELF
32-bit LSB shared object, Intel 80386, version 1 (SYSV), dynamically
linked, not stripped