Convert GN single-item list concat to use lists.

tools/gn/secondary/net/third_party/nss/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.
 
 config("ssl_config") {
   include_dirs = [
     "//net/third_party/nss/ssl",
   ]
 }
 
@@ skipping 49 matching lines @@
     "ssl/win32err.h",
     "ssl/bodge/secitem_array.c",
   ]
 
   defines = [
     "NO_PKCS11_BYPASS",
     "NSS_ENABLE_ECC",
     "USE_UTIL_DIRECTLY",
   ]
 
-  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 = [ ":ssl_config" ]
 
   if (is_win) {
     sources -= [
       "ssl/unix_err.c",
       "ssl/unix_err.h",
     ]
   } else {
     sources -= [
       "ssl/win32err.c",
       "ssl/win32err.h",
     ]
   }
 
   if (is_linux) {
     include_dirs = [ "bodge" ]
-    configs += "//third_party/nss:nss_linux_config"
+    configs += [ "//third_party/nss:nss_linux_config" ]
   }
   if (is_mac) {
     sources -= "ssl/bodge/secitem_array.c"
   }
 }