[ocaml-platform] Getting a macports gmp to interact with opam

[Watson Ladd]

Dear all,

I have gmp living in /opt/local/include and /opt/local/lib, and it
works. However, opam doesn't recognize it, and so I cannot install
why3, without which frama-c is quite impoverished. How do I pass the
location of other directories to search for prerequisites?

Thank you for your assistance.

Sincerely,
Watson Ladd