With cross.patch I've been able to build a working freebsd
python on linux.

Since you had little problems with the X-compile patches, I'm
resubmitting those first.  I'd like to give our (admittedly: oddball)
mingw version another go when the X-compile patches are in python SVN.

Regarding your comments:

* what would be a better to import the SO setting?

the most reliable way to get something out of a makefile into python is

  VAR=foo
  export VAR
  .. 
  os.environ['VAR']

this doesn't introduce any fragility in parsing/expanding/(un)quoting, so it's
actually pretty good.

Right now, I'm overriding sysconfig wholesale in setup.py with a

  sysconfig._config_vars.update (os.environ)

but I'm not sure that this affects the settings in build_ext.py.
A freebsd -> linux compile does not touch that code, so
if you dislike it, we can leave it out.

* I've documented the .x  extension

File Added: cross.patch