Export words function

It will now be generated in mk2rbc as part of
foreach expressions.

Bug: 201700692
Test: None
Change-Id: I400563946d46d7cac9be901a80470248990800bd
diff --git a/core/product_config.rbc b/core/product_config.rbc
index f26b428..39f9189 100644
--- a/core/product_config.rbc
+++ b/core/product_config.rbc
@@ -748,4 +748,5 @@
     setdefault = _setdefault,
     shell = rblf_shell,
     warning = _mkwarning,
+    words = __words,
 )