Better error when 'open'ing a module aliased to a functor.

Consider:

    module F(X : sig end) = struct end
    module G = F
    open G

Before this PR:

   Error: This module is not a structure; it has type (module F)

After:

   Error: This module is not a structure; it has type
          functor (X : sig  end) -> sig  end

* Apply the fix from ocaml#829 to asmcomp

* Turn warnings on in comballoc and make match exhaustive

…#830)

* Apply the fix from ocaml#829 to asmcomp

* Turn warnings on in comballoc and make match exhaustive

25188da flambda-backend: Missed comment from PR802 (ocaml#887)
9469765 flambda-backend: Improve the semantics of asynchronous exceptions (new simpler version) (ocaml#802)
d9e4dd0 flambda-backend: Fix `make runtest` on NixOS (ocaml#874)
4bbde7a flambda-backend: Simpler symbols (ocaml#753)
ef37262 flambda-backend: Add opaqueness to Obj.magic under Flambda 2 (ocaml#862)
a9616e9 flambda-backend: Add build system hooks for ocaml-jst (ocaml#869)
045ef67 flambda-backend: Allow the compiler to build with stock Dune (ocaml#868)
3cac5be flambda-backend: Simplify Makefile logic for natdynlinkops (ocaml#866)
c5b12bf flambda-backend: Remove unnecessary install lines (ocaml#860)
ff12bbe flambda-backend: Fix unused variable warning in st_stubs.c (ocaml#861)
c84976c flambda-backend: Static check for noalloc: attributes (ocaml#825)
ca56052 flambda-backend: Build system refactoring for ocaml-jst (ocaml#857)
39eb7f9 flambda-backend: Remove integer comparison involving nonconstant polymorphic variants (ocaml#854)
c102688 flambda-backend: Fix soundness bug by using currying information from typing (ocaml#850)
6a96b61 flambda-backend: Add a primitive to enable/disable the tick thread (ocaml#852)
f64370b flambda-backend: Make Obj.dup use a new primitive, %obj_dup (ocaml#843)
9b78eb2 flambda-backend: Add test for ocaml#820 (include functor soundness bug) (ocaml#841)
8f24346 flambda-backend: Add `-dtimings-precision` flag (ocaml#833)
65c2f22 flambda-backend: Add test for ocaml#829 (ocaml#831)
7b27a49 flambda-backend: Follow-up PR#829 (comballoc fixes for locals) (ocaml#830)
ad7ec10 flambda-backend: Use a custom condition variable implementation (ocaml#787)
3ee650c flambda-backend: Fix soundness bug in include functor (ocaml#820)
2f57378 flambda-backend: Static check noalloc (ocaml#778)
aaad625 flambda-backend: Emit begin/end region only when stack allocation is enabled (ocaml#812)
17c7173 flambda-backend: Fix .cmt for included signatures (ocaml#803)
e119669 flambda-backend: Increase delays in tests/lib-threads/beat.ml (ocaml#800)
ccc356d flambda-backend: Prevent dynamic loading of the same .cmxs twice in private mode, etc. (ocaml#784)
14eb572 flambda-backend: Make local extension point equivalent to local_ expression (ocaml#790)
487d11b flambda-backend: Fix tast_iterator and tast_mapper for include functor. (ocaml#795)
a50a818 flambda-backend: Reduce closure allocation in List (ocaml#792)
96c9c60 flambda-backend: Merge ocaml-jst
a775b88 flambda-backend: Fix ocaml/otherlibs/unix 32-bit build (ocaml#767)
f7c2679 flambda-backend: Create object files internally to avoid invoking GAS (ocaml#757)
c7a46bb flambda-backend: Bugfix for Cmmgen.expr_size with locals (ocaml#756)
b337cb6 flambda-backend: Fix build_upstream for PR749 (ocaml#750)
8e7e81c flambda-backend: Differentiate is_int primitive between generic and variant-only versions (ocaml#749)

git-subtree-dir: ocaml
git-subtree-split: 25188da