Fix 32-bit build (ocaml-flambda#138)

Add flambda2 to build_ocaml_compiler.sexp, part 2

Add Flambda 2 CI workflow (ocaml-flambda#116)

Revert VERSION, etc. back to 4.12.0 (mostly reverts 822d0a0 from upst…

…ream 4.12) (ocaml-flambda#93)

Gc.set incorrectly handles the three `custom_*` fields (#10125) (ocam…

…l-flambda#43)

Some `Long_val` conversions were missing.

This was setting the wrong values for the `custom_` parameters,
causing the major GC to work too much, slowing down some programs.

Add regression test.

Fixes: #9326

Co-authored-by: Xavier Leroy <[email protected]>

Fix integer literal that is too big for 32-bit targets (ocaml-flambda#39

)

Fix error "integer literal exceeds the range of representable integers
of type nativeint" in the code that runs only on 64-bit targets, but
need to compile on 32-bit target.

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