Work on Mac GN build

tools/gn/secondary/third_party/icu/BUILD.gn

 # Copyright (c) 2012 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.
 
 # Meta target that includes both icuuc and icui18n. Most targets want both.
 # You can depend on the individually if you need to.
 group("icu") {
   deps = [
     ":icui18n",
     ":icuuc",
@@ skipping 205 matching lines @@
     "//build/config/compiler:no_rtti",  # ICU uses RTTI.
     "//build/config/compiler:chromium_code",
   ]
   configs += [
     "//build/config/compiler:rtti",
     "//build/config/compiler:no_chromium_code",
   ]
 
   configs += [ ":icu_code" ]
   direct_dependent_configs = [ ":icu_config" ]
+
+  if (is_clang) {
+    # uspoof.h has a U_NAMESPACE_USE macro. That's a bug,
+    # the header should use U_NAMESPACE_BEGIN instead.
+    # http://bugs.icu-project.org/trac/ticket/9054
+    configs -= [ "//build/config/clang:extra_warnings" ]
+
+    cflags = [
+      "-Wno-header-hygiene",
+      # Looks like a real issue, see http://crbug.com/114660
+      "-Wno-return-type-c-linkage",
+    ]
+  }
 }
 
 component("icuuc") {
   sources = [
     "source/common/bmpset.cpp",
     "source/common/brkeng.cpp",
     "source/common/brkiter.cpp",
     "source/common/bytestream.cpp",
     "source/common/caniter.cpp",
     "source/common/chariter.cpp",
@@ skipping 185 matching lines @@
       # the icudt46_dat symbol.
       "android/icudt46l_dat.S",
       "linux/icudt46l_dat.S",
       "mac/icudt46l_dat.S",
     ]
     defines = [ "U_HIDE_DATA_SYMBOL" ]
 
     # TODO(brettw) support use_system_icu and icu_use_data_file_flag.
   }
 }