libgit2: fix darwin build

pkgs/development/libraries/git2/default.nix

@@ -1,4 +1,7 @@
-{ stdenv, fetchFromGitHub, pkgconfig, cmake, zlib, python, libssh2, openssl, curl, http-parser, libiconv }:
+{ stdenv, fetchFromGitHub, pkgconfig, cmake
+, zlib, python, libssh2, openssl, curl, http-parser
+, libiconv, Security
+}:
 
 stdenv.mkDerivation (rec {
   name = "libgit2-${version}";
@@ -12,11 +15,14 @@ stdenv.mkDerivation (rec {
     sha256 = "0zrrmfkfhd2xb4879z5khjb6xsdklrm01f1lscrs2ks68v25fk78";
   };
 
-  cmakeFlags = "-DTHREADSAFE=ON";
+  cmakeFlags = [ "-DTHREADSAFE=ON" ];
 
   nativeBuildInputs = [ cmake python pkgconfig ];
 
-  buildInputs = [ zlib libssh2 openssl http-parser curl ];
+  buildInputs = [ zlib libssh2 openssl http-parser curl ]
+    ++ stdenv.lib.optional stdenv.isDarwin Security;
+
+  propagatedBuildInputs = stdenv.lib.optional (!stdenv.isLinux) [ libiconv ];
 
   enableParallelBuilding = true;
 
@@ -27,6 +33,4 @@ stdenv.mkDerivation (rec {
     platforms = with platforms; all;
   };
 } // stdenv.lib.optionalAttrs (!stdenv.isLinux) {
-  NIX_LDFLAGS = "-liconv";
-  propagatedBuildInputs = [ libiconv ];
 })