title: Nix: how to change stdenv in nixpkgs.mkShell
body: <p>I'd like to override the stdenv for <code>mkShell</code> to use gcc10Stdenv. I've looked at <a href="https://nixos.wiki/wiki/Using_Clang_instead_of_GCC" rel="nofollow noreferrer">https://nixos.wiki/wiki/Using_Clang_instead_of_GCC</a>, which provides instructions for overriding stdenv, but it doesn't describe how to do it for <code>mkShell</code> when just making a shell without reference to any specific package (only for &quot;Using Nix CLI on existing packages&quot;).</p>
  <p>My question is whether it's possible to override stdenv for mkShell without an existing package? And if so, how?</p>