diff -r 6a938ce6315c Lib/sysconfig.py
--- a/Lib/sysconfig.py	Wed Oct 17 06:15:40 2012 -0400
+++ b/Lib/sysconfig.py	Wed Oct 17 07:34:09 2012 -0400
@@ -396,25 +396,30 @@
     # `make pybuilddir.txt` target -- which is a precursor to the
     # _sysconfigdata.py module being constructed.  Unfortunately,
     # get_config_vars() eventually calls _init_posix(), which attempts
-    # to import _sysconfigdata, which we won't have built yet.  So,
-    # write out _sysconfigdata.py to the current directory first,
-    # then call get_platform() to get the pybuilddir, then move it.
-    destfile = '_sysconfigdata.py'
+    # to import _sysconfigdata, which we won't have built yet.  In order
+    # for _init_posix() to work, if we're on Darwin, just mock up the
+    # _sysconfigdata module manually and populate it with the build vars.
+    # This is more than sufficient for ensuring the subsequent call to
+    # get_platform() succeeds.
+    name = '_sysconfigdata'
+    if 'darwin' in sys.platform:
+        import imp
+        module = imp.new_module(name)
+        module.build_time_vars = vars
+        sys.modules[name] = module
+
+    pybuilddir = 'build/lib.%s-%s' % (get_platform(), sys.version[:3])
+    if hasattr(sys, "gettotalrefcount"):
+        pybuilddir += '-pydebug'
+    os.makedirs(pybuilddir, exist_ok=True)
+    destfile = os.path.join(pybuilddir, name + '.py')
+
     with open(destfile, 'w', encoding='utf8') as f:
         f.write('# system configuration generated and used by'
                 ' the sysconfig module\n')
         f.write('build_time_vars = ')
         pprint.pprint(vars, stream=f)
 
-    pybuilddir = 'build/lib.%s-%s' % (get_platform(), sys.version[:3])
-    if hasattr(sys, "gettotalrefcount"):
-        pybuilddir += '-pydebug'
-    os.makedirs(pybuilddir, exist_ok=True)
-    target = os.path.join(pybuilddir, destfile)
-
-    # Relocate _sysconfigdata.py into its final home.
-    os.rename(destfile, target)
-
     # Create file used for sys.path fixup -- see Modules/getpath.c
     with open('pybuilddir.txt', 'w', encoding='ascii') as f:
         f.write(pybuilddir)