Fix build compatibility with old versions of `gcc` (#3579)

Make the build work under old versions of `gcc` that don't support the `retain` attribute

Bump magic numbers for 5.2.0minus-5 (#3478)

Fix cldemote for Cfg_selection (#3329)

Fix the kind of poison constants generated for unboxed value slots (#…

…3291)

fix assert in the debug runtime

Make `flambda_backend_objinfo.ml` easier to diff with upstream (#3167)

Fix `-stop-after lambda` (#3128)

Stop counting immediates as part of the non-scannable suffix (to stop…

… misleading the optimizer) (#3100)

* Add regression test (it raises caml_flambda2_invalid at runtime in native code)

* Fix test

* Expected change to test

(cherry picked from commit 5a46c46)

Bump magic numbers for 5.1.1minus-24 (#3054)

Fix bug with update_field and mixed blocks (#3028)