Made distutils understand the MacPython Carbon runtime model. Distutils will build for the runtime model you are currently using for the interpreter.
diff --git a/Lib/distutils/mwerkscompiler.py b/Lib/distutils/mwerkscompiler.py
index 2edc825..981fd95 100644
--- a/Lib/distutils/mwerkscompiler.py
+++ b/Lib/distutils/mwerkscompiler.py
@@ -114,6 +114,8 @@
         # into the project.
         if output_filename[-8:] == '.ppc.slb':
             basename = output_filename[:-8]
+        elif output_filename[-11:] == '.carbon.slb':
+            basename = output_filename[:-11]
         else:
             basename = os.path.strip(output_filename)[0]
         projectname = basename + '.mcp'