Add BUILD.gn for third_party/yasm.

build/gn_helper_scripts.gni

+# 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.
+
+template("run_executable") {
+  action("${target_name}") {
+    script = "//build/gn_run_binary.py"
+
+    if (defined(invoker.sources)) {
+      sources = invoker.sources
+    }
+    if (defined(invoker.outputs)) {
+      outputs = invoker.outputs
+    }
+    if (defined(invoker.source_prereqs)) {
+      source_prereqs = invoker.source_prereqs
+    }
+
+    args = [
+      host_toolchain,
+      current_toolchain,
+      rebase_path(root_out_dir + "/" + invoker.binary_name, root_build_dir)
+    ]
+    if (defined(invoker.args)) {
+      args += invoker.args
+    }
+
+    if (defined(invoker.datadeps)) {
+      datadeps += invoker.datadeps
+    }
+    if (defined(invoker.deps)) {
+      deps = invoker.deps
+    }
+  }
+}
+
+template("run_executable_foreach") {
+  action_foreach("${target_name}") {
+    script = "//build/gn_run_binary.py"
+    sources = invoker.sources
+    if (defined(invoker.outputs)) {
+      outputs = invoker.outputs
+    }
+    if (defined(invoker.source_prereqs)) {
+      source_prereqs = invoker.source_prereqs
+    }
+
+    args = [
+      host_toolchain,
+      current_toolchain,
+      rebase_path(root_out_dir + "/" + invoker.binary_name, root_build_dir)
+    ]
+    if (defined(invoker.args)) {
+      args += invoker.args
+    }
+
+    if (defined(invoker.datadeps)) {
+      datadeps += invoker.datadeps
+    }
+    if (defined(invoker.deps)) {
+      deps = invoker.deps
+    }
+  }
+}
+