Fix read_cma

[art-w]

A quick fix to compile ppxlib with the ocaml trunk, as the Cmo_format.cu_name is now a newtype since ocaml/ocaml#12031

https://github.com/ocaml/ocaml/blob/7810957dec3137ad386bd529c32e61659102398c/file_formats/cmo_format.mli#L20-L21

[hhugo]

Can we have a new opam release with ocaml 5.2 support ? I'm surprised this was merged without some sort of conditional compilation to support OCaml version < 5.2

[ccasin]

Can we have a new opam release with ocaml 5.2 support ? I'm surprised this was merged without some sort of conditional compilation to support OCaml version < 5.2

I believe @dkalinichenko-js is working on a new release of our libraries, but I do not know if it supports ocaml 5.2.

[hhugo]

The last release of ocaml-compiler-libs is 3 years old, I'm not sure it is released like other packages.
The master branch works fine with ocaml 5.2 (thanks to this PR) but won't work on older ocaml compilers.

[art-w]

Yeah hm, considering that ocaml-compiler-libs had been very stable until now, I felt it would be simple enough to let the opam solver choose which version of this package is compatible with the current switch. Do you need to set a hard version on ocaml-compiler-libs or do you plan to add new features? (the opam bound isn't future proof, I can add some conditional compilation if preferred)

[dkalinichenko-js]

I've submitted a PR with a new release v0.17.0 for 5.2 and above here. I think this is sufficient for the opam solver to choose the right version. We don't really plan to add new features to this library, so there's no need for conditional compilation.