Copy kernel module source including subfolders

Previously the build used the GN copy() target to copy the source
of a to-be-built kernel module into the output directory. However,
the target does not support preserving subfolder structure. Replace
it with a Python script.

A new 'source_dir_copy' template is added, which creates a dependency
on the files in the source directory using the 'source_dir' target.
Then it copies the files into 'target_out_dir'. When the source
directory changes, the copying Python script is invoked again, updating
the copy in the out folder.

Change-Id: I23f2807fbb77bcf6d933e9541f5dbf1f2429b410
diff --git a/build/linux/copy_dirs.py b/build/linux/copy_dirs.py
new file mode 100644
index 0000000..e44128e
--- /dev/null
+++ b/build/linux/copy_dirs.py
@@ -0,0 +1,52 @@
+#!/usr/bin/env python
+#
+# Copyright 2019 The Hafnium Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+#!/usr/bin/env python
+"""Copies all files inside one folder to another, preserving subfolders."""
+
+import argparse
+import os
+import shutil
+import sys
+
+def main():
+	parser = argparse.ArgumentParser()
+	parser.add_argument("source_folder",
+	                    help="directory to be copied from")
+	parser.add_argument("destination_folder",
+	                    help="directory to be copied into")
+	parser.add_argument("stamp_file",
+	                    help="stamp file to be touched")
+	args = parser.parse_args()
+
+	# Walk the subfolders of the source directory and copy individual files.
+	# Not using shutil.copytree() because it never overwrites files.
+	for root, _, files in os.walk(args.source_folder):
+		for f in files:
+			abs_src_path = os.path.join(root, f)
+			rel_path = os.path.relpath(abs_src_path, args.source_folder)
+			abs_dst_path = os.path.join(args.destination_folder, rel_path)
+			abs_dst_folder = os.path.dirname(abs_dst_path)
+			if not os.path.isdir(abs_dst_folder):
+				os.makedirs(abs_dst_folder)
+			shutil.copyfile(abs_src_path, abs_dst_path)
+
+	# Touch `stamp_file`.
+	with open(args.stamp_file, "w"):
+		pass
+
+if __name__ == "__main__":
+    sys.exit(main())