Should distutils rely on sysconfig for LDSHARED etc?

#36 raises a design question: should distutils-as-an-independent-module be relying on the Python interpreter's sysconfigdata variables to know how to compile and link extensions? In the specific case of #36, there's no real reason why distutils couldn't decide at runtime, based on MACOSX_DEPLOYMENT_TARGET, whether to use -undefined dynamic_lookup or link against the framework explicitly, rather than erroring when the sysconfig and runtime targets differ.

Bringing in an equivalent of the checks cpython does at configure time to figure out the right values for all the relevant variables on each platform is of course going to be a much more daunting task. But it might ultimately be a better approach? I don't know what the right answer is here, but I think it's something that needs to be thought about.

Start by reading issue #36 and tracing how distutils uses the Python interpreter's sysconfigdata variables for LDSHARED and related compile/link settings. Compare that behavior with the runtime MACOSX_DEPLOYMENT_TARGET case described here and with CPython's configure-time checks. Done means reaching and documenting a decision about whether independent distutils should retain sysconfig values or derive them at runtime across platforms.