Fix ocaml-ssl in nnpchecker mode

[kit-ty-kate]

Detected in ocaml/opam-repository#22363 (comment)
and debugged using rr as described in https://discuss.ocaml.org/t/ann-a-dynamic-checker-for-detecting-naked-pointers/5805 to find that the pointer came from ocaml-ssl

[anmonteiro]

To help me understand, does the following make sense?

• the code is already compatible with "no naked pointers" (default in 5.0)
• there's a version of the compiler that checks naked pointers, which defines this different NAKED_POINTERS_CHECKER

[kit-ty-kate]

Yes, nnpchecker has been an option since OCaml 4.12. Technically what it does is:

• allow naked pointer
• but add an extra check to detect uses of naked pointer, print them to make them debuggable
• and make the program fail if it encountered one (since OCaml 4.13, useful for CI)

[anmonteiro]

Awesome -- thank you!