Add BUILD.gn for third_party/yasm.

build/gn_run_binary.py

Index: build/gn_run_binary.py
diff --git a/build/gn_run_binary.py b/build/gn_run_binary.py
new file mode 100644
index 0000000000000000000000000000000000000000..834401136b74cb8b0d3085877ad8aac0bae3f127
--- /dev/null
+++ b/build/gn_run_binary.py
@@ -0,0 +1,28 @@
+# 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.
+
+"""Helper script for GN to run an arbitrary binary.
+
+Run with:
+  python gn_run_binary.py <host_toolchain> <current_toolchain> \
+      <binary_name> [args ...]
+"""
+
+import sys
+import subprocess
+
+if sys.argv[1] == sys.argv[2]:
+  path = './'
+else:
+  # If cross-compiling, binaries for the host toolchain is prefixed by the
+  # toolchain definition name which is everything after the last colon in the
+  # toolcahin identifier.
+  host_toolchain_dir = sys.argv[1].split(':')[-1]
+  assert(host_toolchain_dir)
+  path = './' + host_toolchain_dir + '/'
+
+args = [ path + sys.argv[3] ]
+args.extend(sys.argv[4:])
+
+subprocess.call(args)