I had a patch that only changed distutils.sysconfig.get_config_var('CFLAGS') when not building python, but then noticed that this doesn't work: the setup.py file for stdlib extensions fetches information from the toplevel sysconfig file, not distutils.sysconfig and uses that to override some information (look for "make CC=altcc").

There are two problems there, for which I'll file separate issues:

1) setup.py shouldn't use sysconfig but distutils.sysconfig

2) the block of code that I mentioned earlier is not necessary at all, the comment is plain wrong (tested by removing the compiler update and running 'make CC=no-such-file')

V2 of the hack triggers the change of BASECFLAGS only when not building the stdlib, but that doesn't work right now because of the issues mentioned earlier.