Lambda and Clambda distinguish Const_int from Const_pointer only so
that they can pass the information to Cmm. But now that that
Const_pointer is gone from Cmm (#9578), there's no need for the
distinction in Lambda either.
This PR requires a bootstrap, because the .cmo format changes:
Lambda.structured_constant has one fewer constructor. The bootstrap
is in the following commit.
* Various file moves in the middle end: this is the first stage of improving separation between the middle end and backend.
* Creation of file_formats/ directory (with associated file moves) to hold the definitions of compilation artifact formats.
* Creation of lambda/ directory (with associated file moves) to hold Lambda language definition files, transformation passes and construction passes from Typedtree.
* Disable (hopefully temporarily) dynlink, debugger and ocamldoc for the dune build.