Merge cgTailCall and cgLneJump into one function

Previosly logic of these functions was sth like this:

  cgIdApp x = case x of
                A -> cgLneJump
                _ -> cgTailCall x

  cgTailCall x = case x of
                   B -> ...
                   C -> ...
                   _ -> ...

After merging there is no nesting of cases:

  cgIdApp x = case x of
                A -> cgLneJump
                B -> ...
                C -> ...
                _ -> ...