cctools-binutils-darwin/bin/ranlib failed, malformed object (unknown load command) - macos

Question

I am attempting to build the gitlib-libgit2 Haskell package on macos via nix in roughly the following manner.
mkdir nix-repro && cd nix-repro
cabal2nix --no-check cabal://gitlib-libgit2 > gitlib-libgit2.nix
echo '(import <nixpkgs> {}).haskellPackages.callPackage ./gitlib-libgit2.nix {}' > default.nix
nix-build
I am seeing the following warnings and error:
ld: warning: /nix/store/spx9xz1jv3yhmqw8y3agki1fvdr2x2fv-libiconv-osx-10.11.6/lib/libiconv.dylib, ignoring unexpected dylib file
ld: warning: /nix/store/spx9xz1jv3yhmqw8y3agki1fvdr2x2fv-libiconv-osx-10.11.6/lib/libiconv.dylib, ignoring unexpected dylib file
/nix/store/s33984hx2gwcg2d4dgpcm4342md19qvh-cctools-binutils-darwin/bin/ranlib: object: dist/build/libHSgitlib-libgit2-3.1.2.1-1fYQZMedHRP3aXiBXJFDO2-ghc8.6.3.a(s2_meth.o) malformed object (unknown load command 1)
`ranlib' failed in phase `Ranlib'. (Exit code: 1)
builder for '/nix/store/yrran1p69pvdq1b34jqfq7dmd95j9fh9-gitlib-libgit2-3.1.2.1.drv' failed with exit code 1
error: build of '/nix/store/yrran1p69pvdq1b34jqfq7dmd95j9fh9-gitlib-libgit2-3.1.2.1.drv' failed
What does this mean, and how can I go about fixing it?
It only fails this way on macos, as far as I can tell. I'm on nixpkgs-unstable. I am able to build this package using other tools, so the failure must be something specific to the nix tooling I'm using to build it.
$ cat $HOME/.nix-defexpr/channels/nixpkgs/.git-revision
6e5caa3f8ac48750233ef82a94825be238940825
Here's the full gitlib-libgit2.nix expression if you don't want to run cabal2nix for yourself:
{ mkDerivation, base, bytestring, conduit, conduit-combinators
, containers, directory, exceptions, fast-logger, filepath, gitlib
, gitlib-test, hlibgit2, hspec, hspec-expectations, HUnit, mmorph
, monad-loops, mtl, resourcet, stdenv, stm, stm-conduit, tagged
, template-haskell, text, text-icu, time, transformers
, transformers-base, unliftio, unliftio-core
}:
mkDerivation {
pname = "gitlib-libgit2";
version = "3.1.2.1";
sha256 = "b90e0ad2e7e0f58379e02cbe60d2900c95f0a255c34bd3461f8ee5753a6aa23e";
libraryHaskellDepends = [
base bytestring conduit conduit-combinators containers directory
exceptions fast-logger filepath gitlib hlibgit2 mmorph monad-loops
mtl resourcet stm stm-conduit tagged template-haskell text text-icu
time transformers transformers-base unliftio unliftio-core
];
testHaskellDepends = [
base exceptions gitlib gitlib-test hspec hspec-expectations HUnit
transformers
];
doCheck = false;
description = "Libgit2 backend for gitlib";
license = stdenv.lib.licenses.mit;
}