Add BUILD.gn for third_party/yasm.

build/BUILD.gn

+# Copyright 2014 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.
+
+source_set("gn_helper_scripts") {

[brettw, 2014/05/05 16:46:50]

You don't need this target for python files. You can just exec_script random
ones without this.

[awong, 2014/05/05 19:28:34]

Removed and also removed the datadeps.

Is GN smart enough to run actions if the script changes if you don't declare
this dependency?  IIRC, google3 required you declare various filesets in BUILD
because the dependency graph of the various scripts isn't mineable. For example,
if gn_run_binary.py depends on gn_helpers.py, the target wont' know to rebuild
itself if gn_helpers.py is changed. On the otherhand, if with a bundled datadep,
any change to the scripts in a directory will trigger a rebuild of a target.
This biases away from stale binaries.

[brettw, 2014/05/05 19:31:21]

Yes, the script itself will be part of the deps of the action dependencies.

[brettw, 2014/06/10 21:32:31]

I only responded to part of this. When you exec a script the script itself will
be part of the dependency list. But if that imports something else it won't.
I'll look at this.

+  sources = [
+    "gn_helpers.py",
+    "gn_run_binary.py",
+  ]
+}