Convert GN single-item list concat to use lists.

third_party/re2/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.
 
 gyp_file = "//out/gn_gyp/third_party/re2/re2.gyp"
 
 config("re2_config") {
   include_dirs = [ "." ]
 }
 
@@ skipping 41 matching lines @@
     "util/rune.cc",
     "util/sparse_array.h",
     "util/sparse_set.h",
     "util/stringpiece.cc",
     "util/stringprintf.cc",
     "util/strutil.cc",
     "util/utf.h",
     "util/util.h",
   ]
 
-  configs -= "//build/config/compiler:chromium_code"
-  configs += "//build/config/compiler:no_chromium_code"
+  configs -= [ "//build/config/compiler:chromium_code" ]
+  configs += [ "//build/config/compiler:no_chromium_code" ]
   direct_dependent_configs = [ ":re2_config" ]
 
   deps = [
     "//base/third_party/dynamic_annotations",
   ]
 
   if (is_win) {
     include_dirs = [ "mswin" ]
   } else {
-    sources -= "mswin/stdint.h"
+    sources -= [ "mswin/stdint.h" ]
   }
 }