Motivation for this change

Julia recompiles a precompiled file if the mtime stored in the .ji file differs from the mtime of the .ji file. This doesn't work in Nix because Nix changes the mtime of files in the Nix store to 1.

The exact same situation exists with Python .pyc files and is fixed with this patch. I applied the exact same solution to Julia in this PR.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • Ubuntu
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• [N/A] Determined the impact on package closure size (by running nix path-info -S before and after)
• [N/A] Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.