gistfile1.txt

$ utop
Fatal error: cannot load shared library dlllwt_unix_stubs
Reason: dlopen(dlllwt_unix_stubs.so, 0x000A): tried: 'dlllwt_unix_stubs.so' (no such file), '/usr/local/lib/dlllwt_unix_stubs.so' (no such file), '/usr/lib/dlllwt_unix_stubs.so' (no such file), '/Users/ec/Desktop/dlllwt_unix_stubs.so' (no such file)
zsh: abort      utop

$ opam sw
#  switch                       compiler                    description
   /Users/ec/Work/Code/semgrep  ocaml-base-compiler.4.12.0  /Users/ec/Work/Code/semgrep
   _globals                                                 System-global binaries
→  default                      ocaml-base-compiler.4.13.1  default

$ ocamlfind opt has_sockets.c

$ cc has_sockets.o

$ ./a.out
1

$ cat socket_type_table.c 
#include <stdio.h>

extern int socket_type_table[];

int main()
{
    printf("%i\n", socket_type_table[1]);
    return 0;
}

$ ocamlfind opt -linkpkg -package unix socket_type_table.c 

$ # all successful