Use a stamp file when symlinking in GN work around mtime issues

build/symlink.gni

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Creates a symlink.
 # Args:
 #   source: Path to link to.
 #   output: Where to create the symlink.
 template("symlink") {
   action(target_name) {
     forward_variables_from(invoker,
                            [
                              "deps",
                              "testonly",
                              "visibility",
                            ])
+
+    # Can't use the symlink itself as an output since ninja does not properly
+    # process the symlink's mtime.
+    # https://github.com/ninja-build/ninja/issues/1186
     outputs = [
-      invoker.output,
+      "$target_gen_dir/$target_name.stamp",
     ]
     script = "//build/symlink.py"
     args = [
+      "--touch",
+      rebase_path(outputs[0], root_build_dir),
       "-f",
       rebase_path(invoker.source, get_path_info(invoker.output, "dir")),
       rebase_path(invoker.output, root_build_dir),
     ]
   }
 }
 
 # Creates a symlink from root_build_dir/target_name to |binary_label|. This rule
 # is meant to be used within if (current_toolchain == default_toolchain) blocks
 # and point to targets in the non-default toolchain.
@@ skipping 37 matching lines @@
     }
     source = "$_out_dir/$_name"
 
     _output_name = _name
     if (defined(invoker.output_name)) {
       _output_name = invoker.output_name
     }
     output = "$root_out_dir/$_output_name"
   }
 }