5.2.0minus-3

Merge 5.2.0minus 3 (#119)

* Update import scripts

* Import ocaml sources for ocaml-flambda/flambda-backend@e1efceb89a5

* Automatic merges

* Commit conflicts

* Remove files that were deleted in flambda

* Apply old diff to language_extension

* Resolve conflicts

* Resolve errors outside of merlin-specific code

* Resolve more issues

* Fix more issues

* Update magic number script

* Bump magic numbers

* Promote tests

* Add comments about subdirectory

* Use Ast_helper.Sg.mk