Add an option of using nix-shell instead of nix flake

src/tools/nix-dev-shell/envrc-flake

@@ -0,0 +1,8 @@
+# If you want to use this as an .envrc file to create a shell with necessery components 
+# to develop rustc, use the following command in the root of the rusr checkout:
+#	
+# ln -s ./src/tools/nix-dev-shell/envrc-flake ./.envrc && echo .envrc >> .git/info/exclude
+
+if nix flake show path:./src/tools/nix-dev-shell &> /dev/null; then
+  use flake path:./src/tools/nix-dev-shell
+fi

src/tools/nix-dev-shell/envrc-shell

@@ -0,0 +1,7 @@
+# If you want to use this as an .envrc file to create a shell with necessery components 
+# to develop rustc, use the following command in the root of the rusr checkout:
+#	
+# ln -s ./src/tools/nix-dev-shell/envrc-shell ./.envrc && echo .envrc >> .git/info/exclude
+
+use nix ./src/tools/nix-dev-shell/shell.nix
+

src/tools/nix-dev-shell/shell.nix

@@ -0,0 +1,19 @@
+{ pkgs ? import <nixpkgs> {} }:
+let 
+  x = import ./x { inherit pkgs; };
+in
+pkgs.mkShell {
+  name = "rustc";
+  nativeBuildInputs = with pkgs; [
+    binutils cmake ninja pkg-config python3 git curl cacert patchelf nix
+  ];
+  buildInputs = with pkgs; [
+    openssl glibc.out glibc.static x
+  ];
+  # Avoid creating text files for ICEs.
+  RUSTC_ICE = "0";
+  # Provide `libstdc++.so.6` for the self-contained lld.
+  LD_LIBRARY_PATH = "${with pkgs; lib.makeLibraryPath [
+    stdenv.cc.cc.lib
+  ]}";
+}