Support codesigning on MacOS

Fixes #224

toolchains/cc/cc.nix

@@ -9,12 +9,23 @@ in
 }:
 
 let
+  postLinkSignHook =
+    pkgs.writeTextFile {
+      name = "post-link-sign-hook";
+      executable = true;
 
+      text = ''
+        CODESIGN_ALLOCATE=${pkgs.darwin.cctools}/bin/codesign_allocate \
+          ${pkgs.sigtool}/bin/codesign -f -s - "$linkerOutput"
+      '';
+    };
+  darwinBinutils = pkgs.darwin.binutils.override { inherit postLinkSignHook; };
   darwinCC =
     # Work around https://github.com/NixOS/nixpkgs/issues/42059.
     # See also https://github.com/NixOS/nixpkgs/pull/41589.
     pkgs.wrapCCWith rec {
       cc = pkgs.stdenv.cc;
+      bintools = darwinBinutils;
       extraBuildCommands = with pkgs.darwin.apple_sdk.frameworks; ''
         echo "-Wno-unused-command-line-argument" >> $out/nix-support/cc-cflags
         echo "-isystem ${pkgs.llvmPackages.libcxx}/include/c++/v1" >> $out/nix-support/cc-cflags
@@ -36,10 +47,7 @@ let
         let
           paths =
             if pkgs.stdenv.isDarwin then
-              {
-                cc = (pkgs.overrideCC pkgs.stdenv darwinCC).cc;
-                binutils = pkgs.darwin.binutils;
-              }
+              pkgs.overrideCC pkgs.stdenv darwinCC
             else
               {
                 cc = pkgs.stdenv.cc;