[gn] move gn build into etc (#11577)

.gn

@@ -1,3 +1,3 @@
-buildconfig = "//third_party/build_gn/BUILDCONFIG.gn"
+buildconfig = "//etc/gn/BUILDCONFIG.gn"
 
 check_system_includes = true

etc/gn/BUILDCONFIG.gn

@@ -0,0 +1,41 @@
+#  Copyright (c) 2025, The OpenThread Authors.
+#  All rights reserved.
+#
+#  Redistribution and use in source and binary forms, with or without
+#  modification, are permitted provided that the following conditions are met:
+#  1. Redistributions of source code must retain the above copyright
+#     notice, this list of conditions and the following disclaimer.
+#  2. Redistributions in binary form must reproduce the above copyright
+#     notice, this list of conditions and the following disclaimer in the
+#     documentation and/or other materials provided with the distribution.
+#  3. Neither the name of the copyright holder nor the
+#     names of its contributors may be used to endorse or promote products
+#     derived from this software without specific prior written permission.
+#
+#  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+#  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+#  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+#  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+#  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+#  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+#  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+#  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+#  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE]
+#  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+#  POSSIBILITY OF SUCH DAMAGE.
+#
+
+if (target_os == "") {
+  target_os = host_os
+}
+if (target_cpu == "") {
+  target_cpu = host_cpu
+}
+if (current_cpu == "") {
+  current_cpu = target_cpu
+}
+if (current_os == "") {
+  current_os = target_os
+}
+
+set_default_toolchain("//etc/gn/toolchain:gcc")

etc/gn/toolchain/BUILD.gn

@@ -1,6 +1,30 @@
-# 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.
+#  Copyright (c) 2025, The OpenThread Authors.
+#  All rights reserved.
+#
+#  Redistribution and use in source and binary forms, with or without
+#  modification, are permitted provided that the following conditions are met:
+#  1. Redistributions of source code must retain the above copyright
+#     notice, this list of conditions and the following disclaimer.
+#  2. Redistributions in binary form must reproduce the above copyright
+#     notice, this list of conditions and the following disclaimer in the
+#     documentation and/or other materials provided with the distribution.
+#  3. Neither the name of the copyright holder nor the
+#     names of its contributors may be used to endorse or promote products
+#     derived from this software without specific prior written permission.
+#
+#  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+#  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+#  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+#  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+#  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+#  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+#  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+#  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+#  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE]
+#  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+#  POSSIBILITY OF SUCH DAMAGE.
+#
+
 toolchain("gcc") {
   tool("cc") {
     depfile = "{{output}}.d"

third_party/build_gn/BUILDCONFIG.gn

@@ -1,18 +0,0 @@
-# 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.
-
-if (target_os == "") {
-  target_os = host_os
-}
-if (target_cpu == "") {
-  target_cpu = host_cpu
-}
-if (current_cpu == "") {
-  current_cpu = target_cpu
-}
-if (current_os == "") {
-  current_os = target_os
-}
-
-set_default_toolchain("//third_party/build_gn/toolchain:gcc")

third_party/build_gn/README.md

@@ -1,22 +0,0 @@
-# build_gn
-
-## URL
-
-https://gn.googlesource.com/gn/+/refs/heads/master/examples/simple_build/build
-
-## License
-
-BSD 3-Clause
-
-## License File
-
-[LICENSE](https://gn.googlesource.com/gn/+/refs/heads/master/LICENSE)
-
-## Description
-
-gn is metabuild system that generates ninja files for further compilation 
-
-gn tool requires paths to all the toolchains to be used for compilation, for
-example compiler, linker etc. The toolchains in toolchain/BUILD.gn are from the
-examples repository for gn. BUILDCONFIG.gn is also trimmed down version from
-examples/simple_build/build/