[Distutils] trouble determining source for gcc command arguments

[Robert Altman]

I have two mac os/x computers, each up to date with the same compiler
and environments, yet it appears that distutils is emitting different
gcc arguments.  Specifically, one of the computers is attempting to
compile Mercurial using the -isysoot ... argument, effectively causing
the build process to fail.
Details: os/x 10.7
Python 2.7.2 (installed from 10.7 installer at python.org)
Mercurial source is 2.1
I don't see any environment settings which would cause gcc to use to
-isysroot argument and I cannot determine where else it might be
coming from (it is not in the Mercurial project), so I believe it must
be coming from distutils.

Thanks!

Robert