Also OS X universal builds have many of the characteristics of a cross-build.  In particular, one executable (like the python interpreter) can contain both 32-bit and 64-bit architecture files.  So tests for 32-bit vs 64-bit at build time using the running compiler's arch are problematic.  Another issue is the support for building with an OS X SDK.  Basically, all /usr include and lib file paths used for searching in setup.py need to be prefixed by the SDK path if configured.  There are some holes in this right now.  I plan to fix them soon; it would better to have this issue resolved and applied first.