GN: Fix NaCl IRT build options

build/toolchain/gcc_toolchain.gni

 # 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.
 
 import("//build/config/nacl/config.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/ccache.gni")
 import("//build/toolchain/goma.gni")
 import("//build/toolchain/toolchain.gni")
 
@@ skipping 330 matching lines @@
       # These values need to be passed through unchanged.
       target_os = target_os
       target_cpu = target_cpu
 
       forward_variables_from(invoker,
                              [
                                "is_clang",
                                "is_component_build",
                                "is_nacl_glibc",
                                "use_gold",
+                               "symbol_level",
                              ])
 
       if (defined(invoker.clear_sanitizers) && invoker.clear_sanitizers) {
         is_asan = false
         is_cfi = false
         is_lsan = false
         is_msan = false
         is_syzyasan = false
         is_tsan = false
         is_ubsan = false
@@ skipping 35 matching lines @@
     nm = "${toolprefix}nm"
 
     forward_variables_from(invoker,
                            [
                              "toolchain_cpu",
                              "toolchain_os",
                              "use_gold",
                            ])
   }
 }