The reason for each step is documented in the bash snippet. At the time of development, zarith (a transitive dependency) hard coded the GCC dependency in its build process. Perhaps it shouldn't, but it definitely did and continues to require the symlink on systems without GCC. I submitted a patch to fix this in zarith, but it has not made it to opam yet. See The patch here:

https://forge.ocamlcore.org/tracker/index.php?func=detail&ai...