GN build improvements.

net/third_party/nss/ssl/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 = [ "." ]
 
   if (is_mac || is_win) {
     defines = [ "NSS_PLATFORM_CLIENT_AUTH" ]
   }
@@ skipping 100 matching lines @@
     sources -= [
       "bodge/secitem_array.c",
     ]
     deps = [
       "//third_party/nss:nspr",
       "//third_party/nss:nss",
     ]
     forward_dependent_configs_from = deps
   }
 
-  if (component_mode == "shared_library") {
-    # TODO(brettw) GCC_SYMBOLS_PRIVATE_EXTERN thing.
+  if (!is_win && component_mode == "shared_library") {
+    configs -= [ "//build/config/gcc:symbol_visibility_hidden" ]
   }
 
   if (is_clang) {
     cflags += [
       # See http://crbug.com/138571#c8. In short, sslsecur.c picks up the
       # system's cert.h because cert.h isn't in chromium's repo.
       "-Wno-incompatible-pointer-types",
 
       # There is a broken header guard in /usr/include/nss/secmod.h:
       # https://bugzilla.mozilla.org/show_bug.cgi?id=884072
       "-Wno-header-guard",
     ]
   }
 
   if (is_debug) {
     defines += [ "DEBUG" ]
   }
 }