Always set symbol visibility when compiling with GCC / Clang.

build/secondary/third_party/nss/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.
 
 import("//build/config/linux/pkg_config.gni")
 
 if (is_linux) {
   # This is a dependency on NSS with no libssl. On Linux we use a built-in SSL
   # library but the system NSS libraries. Non-Linux platforms using NSS use the
   # hermetic one in //third_party/nss.
@@ skipping 868 matching lines @@
     ]
 
     configs -= [
       "//build/config/compiler:chromium_code",
       "//build/config/gcc:symbol_visibility_hidden",
     ]
 
     configs += [
       "//build/config/compiler:no_chromium_code",
       "//build/config/compiler:no_size_t_to_int_warning",
+      "//build/config/gcc:symbol_visibility_default",
 
       # nss passes "const char*" through "void*".
       "//build/config/compiler:no_incompatible_pointer_warnings",
       ":nss_static_config_private",
     ]
     public_configs = [ ":nss_static_config" ]
 
     cflags = [
       "-include",
       rebase_path("//third_party/nss/nss/lib/freebl/nss_build_config_mac.h",
@@ skipping 35 matching lines @@
 
     public_deps = [
       ":nspr",
     ]
     deps = [
       ":nspr",
       "//third_party/sqlite",
     ]
   }
 }  # iOS.