devel/ocaml-opam: GNUMake run dependency.

GNUMake is needed to build ocaml, and therefore it is needed by the
opam init command.

PR: 261180
Reported by: fuz
Approved by: hannes@mehnert.org (maintainer)
MFH: 2024Q1

(cherry picked from commit 173b2c2ac99f5372e18feb94d81453d56ba93c67)