Refactor the python system_impl module.

mojo/python/system/mojo/embedder.pyx

Index: mojo/python/system/mojo/embedder.pyx
diff --git a/mojo/python/system/mojo/embedder.pyx b/mojo/python/system/mojo/embedder.pyx
index 5d699c0d84360908abae80cb3712edf08b5bbc62..16ff9afce5ac351c29a70c3de804d6c915b46433 100644
--- a/mojo/python/system/mojo/embedder.pyx
+++ b/mojo/python/system/mojo/embedder.pyx
@@ -8,6 +8,7 @@ from libc.stdint cimport uintptr_t
 from libcpp cimport bool
 
 from mojo import system
+from mojo import system_impl
 
 cdef extern from "third_party/cython/python_export.h":
   pass
@@ -43,6 +44,7 @@ def Init():
       new SimplePlatformSupport()))
   cdef MojoSystemThunks thunks = MojoMakeSystemThunks()
   system.SetSystemThunks(<uintptr_t>(&thunks))
+  system_impl.SetSystemThunks(<uintptr_t>(&thunks))
 
 def ShutdownForTest():
   return ShutdownCEmbedderForTest()