chore: Nix bump to LLVM 15

Also update mdbook dependency hash from nixpkgs bump.

Peeled from https://github.com/leanprover/lean4/pull/2340
to enable LLVM for stage1+ builds.

doc/flake.nix

@@ -27,7 +27,7 @@
         src = inputs.mdBook;
         cargoDeps = drv.cargoDeps.overrideAttrs (_: {
           inherit src;
-          outputHash = "sha256-mhTWHs/bsmm3FH59SkUxBTl5lEH2Rlz/aF9CuBTu1TE=";
+          outputHash = "sha256-1YlPS6cqgxE4fjy9G8pWrpP27YrrbCDnfeyIsX81ZNw=";
         });
         doCheck = false;
       });

flake.lock

@@ -101,11 +101,11 @@
     },
     "nixpkgs_2": {
       "locked": {
-        "lastModified": 1657208011,
-        "narHash": "sha256-BlIFwopAykvdy1DYayEkj6ZZdkn+cVgPNX98QVLc0jM=",
+        "lastModified": 1686089707,
+        "narHash": "sha256-LTNlJcru2qJ0XhlhG9Acp5KyjB774Pza3tRH0pKIb3o=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "2770cc0b1e8faa0e20eb2c6aea64c256a706d4f2",
+        "rev": "af21c31b2a1ec5d361ed8050edd0303c31306397",
         "type": "github"
       },
       "original": {

nix/packages.nix

@@ -5,7 +5,7 @@ let
     ${nix.packages.${system}.default}/bin/nix --experimental-features 'nix-command flakes' --extra-substituters https://lean4.cachix.org/ --option warn-dirty false "$@"
   '';
   # https://github.com/NixOS/nixpkgs/issues/130963
-  llvmPackages = if stdenv.isDarwin then llvmPackages_11 else llvmPackages_14;
+  llvmPackages = if stdenv.isDarwin then llvmPackages_11 else llvmPackages_15;
   cc = (ccacheWrapper.override rec {
     cc = llvmPackages.clang;
     extraConfig = ''

shell.nix

@@ -9,7 +9,7 @@ in { pkgs ? flakePkgs.nixpkgs, pkgsDist ? pkgs }:
   } (rec {
     buildInputs = with pkgs; [
       cmake gmp ccache
-      llvmPackages.llvm  # llvm-symbolizer for asan/lsan
+      flakePkgs.llvmPackages.llvm  # llvm-symbolizer for asan/lsan
     ];
     # https://github.com/NixOS/nixpkgs/issues/60919
     hardeningDisable = [ "all" ];