Refactor SpecConstr to use treat bindings uniformlywip/T21457

This patch, provoked by #21457, simplifies SpecConstr by treating
top-level and nested bindings uniformly (see the new scBind).

* Eliminates the mysterious scTopBindEnv

* Refactors scBind to handle top-level and nested definitions
  uniformly.

* But, for now at least, continues the status quo of not doing
  SpecConstr for top-level non-recursive bindings.  (In contrast
  we do specialise nested non-recursive bindings, although the
  original paper did not; see Note [Local let bindings].)

  I tried the effect of specialising top-level non-recursive
  bindings (which is now dead easy to switch on, unlike before)
  but found some regressions, so I backed off.  See !8135.

It's a pure refactoring.  I think it'll do a better job in a few
cases, but there is no regression test.

0 files changed, 0 insertions, 0 deletions