INLINE pragmas for default methods don't work

This should work:

  class C a where
    f :: (a -> a) -> [a] -> [a]
    {-# INLINE f #-}
    f g xs = reverse (map g (reverse xs))

  instance C Int

Now calling 'f' at Int should inline the code in the default method. Currently it doesn't, because we get

   dmf a d g xs = ...
   rec { dCInt = dmf Int dCInt }

and since dmf is applied to only one arg, but has arity 3, it isn't inlined, which is a bit silly.

If the class has more than one method, everythign works fine. (But I did fix a bug in TcClassDecl which prevented it working find in 6.4.)

Trac metadata

Trac field	Value
Version	6.4.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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Blocking
CC
Operating system	Unknown
Architecture	Unknown