Always set symbol visibility when compiling with GCC / Clang.

ios/third_party/ochamcrest/BUILD.gn

 # Copyright 2016 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/ios/rules.gni")
 
 ios_framework_bundle("ochamcrest") {
   output_name = "OCHamcrest"
 
   testonly = true
@@ skipping 212 matching lines @@
     "src/Source/OCHamcrest.h",
   ]
 
   libs = [
     "Foundation.framework",
     "UIKit.framework",
   ]
 
   configs += [ "//build/config/compiler:enable_arc" ]
   configs -= [ "//build/config/gcc:symbol_visibility_hidden" ]
+  configs += [ "//build/config/gcc:symbol_visibility_default" ]
 }