This is on osx 10.5.3, latest gcc tool chain.

I have $ARCHFLAGS set to "-arch i386" to prevent the OS/X gcc from 
building PPC code (as I don't want/need it) - if I leave this set as-is, 
other applications build without error, intel only.

If I don't unset it, here's the error:

  File "/Users/jesse/open_source/subversion/python-
trunk/Lib/distutils/ccompiler.py", line 697, in compile
self._compile(obj, src, ext, cc_args, extra_postargs, pp_opts)
  File "/Users/jesse/open_source/subversion/python-
trunk/Lib/distutils/unixccompiler.py", line 176, in _compile
compiler_so = _darwin_compiler_fixup(compiler_so, cc_args + 
extra_postargs)
  File "/Users/jesse/open_source/subversion/python-
trunk/Lib/distutils/unixccompiler.py", line 79, in 
_darwin_compiler_fixup
compiler_so = compiler_so + ' ' + os.environ['ARCHFLAGS']
TypeError: can only concatenate list (not "str") to list
make: *** [sharedmods] Error 1

I've attached a possible patch for this which does a .split() on the os.environ['ARCHFLAGS'] variable, which fixes the issue