release_config: various cleanup

- Allow scl and textproto data to coexist for now
- Print warnings to stderr instead of stdout.
- Improve formatting of output
- Set displays the new value for all configs, and what file changed.
- Use prettier error messages for better UX
- put build-flag on the path.

Bug: 328495189
Test: manual
Change-Id: I4c38860c2fb24db5111e0cecf790660a4ff2b8b2

bin/build-flag

@@ -0,0 +1,28 @@
+#!/bin/bash -eu
+#
+# Copyright 2017 Google Inc. All rights reserved.
+#
+# 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
+#
+#     http://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.
+
+source $(cd $(dirname $BASH_SOURCE) &> /dev/null && pwd)/../../make/shell_utils.sh
+require_top
+
+# Save the current PWD for use in soong_ui
+export ORIGINAL_PWD=${PWD}
+export TOP=$(gettop)
+source ${TOP}/build/soong/scripts/microfactory.bash
+
+soong_build_go build-flag android/soong/cmd/release_config/build_flag
+
+cd ${TOP}
+exec "$(getoutdir)/build-flag" "$@"