Add a snapshot of flutter/engine/src/build to our sdk

build/mac/change_mach_o_flags_from_xcode.sh

Index: build/mac/change_mach_o_flags_from_xcode.sh
diff --git a/build/mac/change_mach_o_flags_from_xcode.sh b/build/mac/change_mach_o_flags_from_xcode.sh
new file mode 100755
index 0000000000000000000000000000000000000000..1824f8db52fe7729378eb41726f7c61ad5473a36
--- /dev/null
+++ b/build/mac/change_mach_o_flags_from_xcode.sh
@@ -0,0 +1,15 @@
+#!/bin/sh
+
+# Copyright (c) 2011 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.
+
+# This is a small wrapper script around change_mach_o_flags.py allowing it to
+# be invoked easily from Xcode. change_mach_o_flags.py expects its arguments
+# on the command line, but Xcode puts its parameters in the environment.
+
+set -e
+
+exec "$(dirname "${0}")/change_mach_o_flags.py" \
+     "${@}" \
+     "${BUILT_PRODUCTS_DIR}/${EXECUTABLE_PATH}"