stdenv: update darwin bootstrap tools for llvm11

Build from bdffd0b276.

https://hydra.nixos.org/build/124753463
(cherry picked from commit f4a08349ed43a36ad5489a4ab548fcf0c129215d)

pkgs/stdenv/darwin/default.nix

@@ -23,7 +23,7 @@
   else
     let
       fetch = { file, sha256, executable ? true }: import <nix/fetchurl.nix> {
-        url = "http://tarballs.nixos.org/stdenv-darwin/x86_64/05ef940b94fe76e7ac06ea45a625adc8e4be96f9/${file}";
+        url = "http://tarballs.nixos.org/stdenv-darwin/x86_64/c253216595572930316f2be737dc288a1da22558/${file}";
         inherit (localSystem) system;
         inherit sha256 executable;
       }; in
@@ -32,7 +32,7 @@
       bzip2 = fetch { file = "bzip2"; sha256 = "sha256-K3rhkJZipudT1Jgh+l41Y/fNsMkrPtiAsNRDha/lpZI="; };
       mkdir = fetch { file = "mkdir"; sha256 = "sha256-VddFELwLDJGNADKB1fWwWPBtIAlEUgJv2hXRmC4NEeM="; };
       cpio = fetch { file = "cpio"; sha256 = "sha256-SWkwvLaFyV44kLKL2nx720SvcL4ej/p2V/bX3uqAGO0="; };
-      tarball = fetch { file = "bootstrap-tools.cpio.bz2"; sha256 = "sha256-b65dXbIm6o6s6U8tAiGpR6SMfvfn/VFcZgTHBetJZis="; executable = false; };
+      tarball = fetch { file = "bootstrap-tools.cpio.bz2"; sha256 = "sha256-kRC/bhCmlD4L7KAvJQgcukk7AinkMz4IwmG1rqlh5tA="; executable = false; };
     }
 }: