Happy -g currently requires GlaExts, which means it can't be used
inside fptools/libraries (GlaExts comes from lang, and lang isn't
built yet). So, until I've fixed Happy and everyone has built &
installed the vnew version...
Add a dummy GlaExts module.
This is a TEMPORARY HACK to keep Happy happy during the switchover
period, and will go away before the release.
--- /dev/null
+module GlaExts (module GHC.Exts, Addr(..)) where
+import GHC.Exts
+
+data Addr = A# Addr# deriving (Eq, Ord)