Fix GN deadlock on error handling.

tools/gn/secondary/base/BUILD.gn

 # Copyright (c) 2013 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.
 
 component("base") {
   external = true
   sources = [
     "../build/build_config.h",
     "third_party/dmg_fp/dmg_fp.h",
     "third_party/dmg_fp/g_fmt.cc",
@@ skipping 769 matching lines @@
 
   # Linux.
   if (is_linux) {
     # TODO(brettw) these will need to be parameterized at some point.
     linux_configs = [
       "//build/config/linux:glib",
       "//build/config/linux:gtk",
       "//build/config/linux:x11",
     ]
     configs += linux_configs
-    all_dependent_configs += linux_configs
+    all_dependent_configs = linux_configs
 
     deps += [
       "//base/third_party/symbolize",
       "//base/third_party/xdg_mime",
       "//base/third_party/xdg_user_dirs",
     ]
   } else {
     # Non-Linux.
     sources -= [
       "message_loop/message_pump_glib.cc",
@@ skipping 225 matching lines @@
 static_library("run_all_unittests") {
   external = true
   sources = [
     "test/run_all_unittests.cc",
   ]
   deps = [
     ":test_support_base",
   ]
 }