adding a minimum ocaml compiler requirement to unison: how?

[Ignatios Souvatzis <is%netbsd.org@localhost>]

Hello,

background: a while ago, I patched the native ARM backend of lang/ocaml
so that code generated by ocamlopt would not SIGILL on thumbless CPUs.

Now, I wanted to teach net/unison to use the native compiler also 
for arm. To make sure that only a sufficiently patched compiler is
used, I wanted it to depend on ocaml>=3.12.0nb2

lang/ocaml/buildlink3.mk contains:

BUILDLINK_API_DEPENDS.ocaml+=   ocaml>=3.08.2
BUILDLINK_ABI_DEPENDS.ocaml+=   ocaml>=3.09.1nb2


I tried 

DEPENDS+=ocaml>=3.12.0nb2:../../lang/ocaml

I tried 

BUILDLINK_ABI_DEPENDS.ocaml+=   ocaml>=3.12.0nb2

and even using BUILDLINK_API_DEPENDS.ocaml.

Whatever I do, make always results in

=> Build dependency ocaml>=3.09.1nb2: found ocaml-3.12.0nb2

That is, in a tree with a compiler that's too old it would nevertheless
build.

So, what should I do?

Regards,
        -is