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

build/config/gcc/BUILD.gn

+# 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.
+
+# This config causes functions not to be automatically exported from shared
+# libraries. By default, all symbols are exported but this means there are
+# lots of exports that slow everything down. In general we explicitly mark
+# which functiosn we want to export from components.
+#
+# Some third_party code assumes all functions are exported so this is separated
+# into its own config so such libraries can remove this config to make symbols
+# public again.
+#
+# See http://gcc.gnu.org/wiki/Visibility
+config("symbol_visibility_hidden") {
+  # Note that -fvisibility-inlines-hidden is set globally in the compiler
+  # config since that can almost always be applied.
+  cflags = [ "-fvisibility=hidden" ]
+}
+
+# Settings for executables and shared libraries.
+config("executable_ldconfig") {
+  if (is_android) {
+    ldflags = [
+      "-Bdynamic",
+      "-Wl,-z,nocopyreloc",
+    ]
+  } else {
+    # Android doesn't support rpath.
+    ldflags = [
+      # Want to pass "\$". GN will re-escape as required for ninja.
+      "-Wl,-rpath=\$ORIGIN/",
+      "-Wl,-rpath-link=",
+
+      # Newer binutils don't set DT_RPATH unless you disable "new" dtags
+      # and the new DT_RUNPATH doesn't work without --no-as-needed flag.
+      "-Wl,--disable-new-dtags",
+    ]
+  }
+}
+
+config("no_exceptions") {
+  no_exceptions_flags = [ "-fno-exceptions" ]
+  cflags_cc = no_exceptions_flags
+  cflags_objcc = no_exceptions_flags
+}