overlay.nix: use no io-testuite enabled package for darwin

This makes it not pick-up linux-namespaces dependency which
is Linux specific.

Author: sorki

overlay.nix

@@ -2,10 +2,13 @@ pkgs: hlib: helf: huper: {
   hnix-store-core =
     helf.callCabal2nix "hnix-store-core" ./hnix-store-core {};
   hnix-store-remote =
-    ( helf.callCabal2nixWithOptions "hnix-store-remote" ./hnix-store-remote "-fio-testsuite" { }
-    ).overrideAttrs (attrs: {
-        buildInputs = attrs.buildInputs ++ [
-          pkgs.nix
-        ];
-    });
+    if pkgs.stdenv.isDarwin
+    then helf.callCabal2nix "hnix-store-remote" ./hnix-store-remote { }
+    else
+      ( helf.callCabal2nixWithOptions "hnix-store-remote" ./hnix-store-remote "-fio-testsuite" { }
+      ).overrideAttrs (attrs: {
+          buildInputs = attrs.buildInputs ++ [
+            pkgs.nix
+          ];
+      });
 }