gn/linux: warnings as errors, turn on Wextra

build/secondary/third_party/icu/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.
 
 declare_args() {
   # Tells icu to load an external data file rather than rely on the icudata
   # being linked directly into the binary.
   #
   # This flag is a bit confusing. As of this writing, icu.gyp set the value to
   # 0 but common.gypi sets the value to 1 for most platforms (and the 1 takes
@@ skipping 240 matching lines @@
     "//build/config/compiler:chromium_code",
   ]
   configs += [
     "//build/config/compiler:rtti",
     "//build/config/compiler:no_chromium_code",
   ]
 
   configs += [ ":icu_code" ]
   direct_dependent_configs = [ ":icu_config" ]
 
+  cflags = []
+  if (is_android || is_linux) {
+    cflags += [
+      # ICU uses its own deprecated functions.
+      "-Wno-deprecated-declarations",
+    ]
+  }
   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 = [
+    cflags += [
       "-Wno-header-hygiene",
       # Looks like a real issue, see http://crbug.com/114660
       "-Wno-return-type-c-linkage",
     ]
   }
 }
 
 component("icuuc") {
   sources = [
     "source/common/appendable.cpp",
@@ skipping 231 matching lines @@
         sources = [ "mac/icudtl_dat.S" ]
       } else if (is_android) {
         sources = [ "android/icudtl_dat.S" ]
       } else {
         assert(false, "No icu data for this platform")
       }
       defines = [ "U_HIDE_DATA_SYMBOL" ]
     }
   }
 }