Set NOSV_HOME for clang wrapped with nodes

This is needed since nosv must appear as a 1rst level dependency on the
final executable. Clang will add the dependency as long as it knows
where to find nosv (and nodes is used).

Reviewed-By: Rodrigo Arias Mallo <rodrigo.arias@bsc.es>

pkgs/nodes/default.nix

@@ -84,4 +84,8 @@ in
       nosv
       ovni
     ];
+
+    passthru = {
+      nosv = nosv;
+    };
   }