openbsd.mkDerivation: add extraNativeBuildInputs input

Some packages require extra hooks or tools.
Rather than overriding all of the nativeBuildInputs
and needing to specify all of them, add a field so that
we just need to specify inputs that are not always required.

Co-Authored-By: Audrey Dutcher <audrey@rhelmot.io>

pkgs/os-specific/bsd/openbsd/pkgs/mkDerivation.nix

@@ -53,7 +53,7 @@ lib.makeOverridable (
         install
         tsort
         lorder
-      ];
+      ] ++ (attrs.extraNativeBuildInputs or [ ]);
 
       HOST_SH = stdenv'.shell;
 
@@ -93,6 +93,6 @@ lib.makeOverridable (
       dontBuild = true;
     }
     // lib.optionalAttrs stdenv'.hostPlatform.isStatic { NOLIBSHARED = true; }
-    // attrs
+    // (builtins.removeAttrs attrs [ "extraNativeBuildInputs" ])
   )
 )