I found the bug report (closed due to inactivity): ld: warning: /usr/lib/libpthread.dylib, ignoring unexpected dylib file · Issue #7933 · ocaml/ocaml · GitHub
The issue is relevant to me in the context of an iOS project using opam-cross-ios where the main program is in C. I am building the OCaml lib and C stubs with dune with (modes (native object)) which uses -output-complete-obj. iOS does not support dynamic linking for user libraries, so an .so is not an option.