doesn't work on a host with gmp installed in /usr/local

[hannesm]

somehow on FreeBSD at least, with the "normal" thing (no gmp bundled, use the host system one), this fails due to it being unable to find libgmp. I thought pkg_config would be there to do so, but it doesn't work.

log output:

334.729s:#=== ERROR while compiling zarith.1.14+dune+mirage1 ===========================#
334.729s:# context              2.5.1 | freebsd/x86_64 |  | git://git.robur.coop/robur/unikernel-repo.git
334.729s:# path                 /tmp/myswitch/.opam-switch/build/zarith.1.14+dune+mirage1
334.729s:# command              /tmp/myswitch/bin/dune build -p zarith
334.729s:# exit-code            1
334.729s:# env-file             /tmp/opam-root-83812/zarith-83812-ce6708.env
334.729s:# output-file          /tmp/opam-root-83812/zarith-83812-ce6708.out
334.729s:### output ###
334.729s:# File "dune", lines 24-29, characters 0-146:
334.729s:# 24 | (rule
334.729s:# 25 |  (target Makefile)
334.729s:# 26 |  (deps configure env)
334.729s:# 27 |  (action
334.729s:# 28 |   (bash
334.729s:# 29 |    "env %{read:env} ./configure --ocamllibdir %{ocaml-config:standard_library}")))
334.729s:# (cd _build/default && /usr/local/bin/bash -e -u -o pipefail -c 'env CC="cc -O2 -fno-strict-aliasing -fwrapv -pthread -fPIC" ./configure --ocamllibdir /tmp/myswitch/lib/ocaml')
334.729s:# binary ocaml: found in /tmp/myswitch/bin
334.729s:# binary ocamlc: found in /tmp/myswitch/bin
334.729s:# binary ocamldep: found in /tmp/myswitch/bin
334.729s:# binary ocamlmklib: found in /tmp/myswitch/bin
334.729s:# binary ocamldoc: found in /tmp/myswitch/bin
334.729s:# binary cc: found in /usr/bin
334.729s:# binary ocamlopt: found in /tmp/myswitch/bin
334.729s:# checking compilation with  : working
334.729s:# include caml/mlvalues.h: found
334.729s:# library dynlink.cmxa: found
334.729s:# binary ocamlfind: found in /tmp/myswitch/bin
334.729s:# OCaml's word size is 64
334.729s:# include gmp.h: not found
334.729s:# include mpir.h: not found
334.729s:# cannot find GMP nor MPIR