1. ppc arch detection for extension module builds broke with Xcode 5
2. ppc arch detection in configure did not work on OS X 10.4
3. -sysroot and -arch flags were unnecessarily duplicated
4. there was no obvious way to configure an intel-32 only build.
tailoring for universal builds by factoring out common OS X-specific
customizations from sysconfig, distutils.sysconfig, distutils.util,
and distutils.unixccompiler into a new module _osx_support that can
eventually also be used by packaging.
