Add entries for the weakref module to the build control.
diff --git a/Modules/Setup.dist b/Modules/Setup.dist
index ea76938..bef4939 100644
--- a/Modules/Setup.dist
+++ b/Modules/Setup.dist
@@ -147,6 +147,7 @@
#struct structmodule.c # binary structure packing/unpacking
#time timemodule.c # -lm # time operations and variables
#operator operator.c # operator.add() and similar goodies
+#_weakref _weakref.c # basic weak reference support
#_codecs _codecsmodule.c # access to the builtin codecs and codec registry
#unicodedata unicodedata.c unicodedatabase.c