add some more comments to explain what i'm thinking

src/python/pants/backend/python/subsystems/python_dist_build_environment.py

@@ -25,6 +25,12 @@ def _native_toolchain(self):
 
   def modify_environment(self, env):
     env = self._native_toolchain.modify_environment(env)
+    # If we're going to be wrapping setup.py-based projects, we really should be
+    # doing it through a subclass of a distutils UnixCCompiler (in Lib/distutils
+    # in the CPython source) instead of hoping setup.py knows what to do. The
+    # default UnixCCompiler from distutils will build a 32/64-bit "fat binary"
+    # unless you use their undocumented ARCHFLAGS env var, and there may be more
+    # dragons later on.
     env['CC'] = 'gcc'
     env['CXX'] = 'g++'
     env['ARCHFLAGS'] = '-arch x86_64'

src/python/pants/backend/python/tasks/build_local_python_distributions.py

@@ -53,7 +53,7 @@ def subsystem_dependencies(cls):
 
   # TODO: seriously consider subclassing UnixCCompiler as well as the build_ext
   # command from distutils to control the compiler and linker invocations
-  # transparently instead of guessing what distutils does by default.
+  # transparently instead of hoping distutils does the right thing.
   @memoized_property
   def _python_dist_build_environment(self):
     return PythonDistBuildEnvironment.scoped_instance(self)