The operator "or" (which has been deprecated for more than 10 years) is used in: mArray.ml:55 prime.ml:87
There is now (in OCaml trunk, soon-to-be 4.01.0) a warning for uses of such deprecated features, and unfortunately you compile with "-warn-error A", which stops compilation when the warning is triggered. This is not recommended for released sources.
Suggested fix: at line 50 of Makefile, replace "-warn-error A" with "-warn-error a" to get better forward-compatibility with future versions of OCaml.
You might also want to replace these "or" with the modern "||".