atexit is a builtin module now, provide that on Windows.
diff --git a/PC/config.c b/PC/config.c
index 68fa84f..38d91de 100644
--- a/PC/config.c
+++ b/PC/config.c
@@ -60,6 +60,7 @@
 extern void init_ast(void);
 extern void init_types(void);
 extern void init_fileio(void);
+extern void initatexit(void);
 
 /* tools/freeze/makeconfig.py marker for additional "extern" */
 /* -- ADDMODULE MARKER 1 -- */
@@ -147,6 +148,7 @@
         
         {"_types", init_types},
         {"_fileio", init_fileio},
+        {"atexit", initatexit},
 
         /* Sentinel */
         {0, 0}