darwin: use llvm’s dsymutil instead of dummy version

We were previously using a dummy wrapper for dsymutil. This meant that
debug symbols were not getting generated when dsymutil was otherwise
available. This should fix that issue & provide a real dsymutil from
llvm.

Fixes #52148.

pkgs/os-specific/darwin/cctools/port.nix

@@ -92,13 +92,6 @@ let
       popd
     '';
 
-    postInstall = ''
-      cat >$out/bin/dsymutil << EOF
-      #!${stdenv.shell}
-      EOF
-      chmod +x $out/bin/dsymutil
-    '';
-
     passthru = {
       inherit targetPrefix;
     };