Remove unnecessary clang flags for 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.
 
 import("//third_party/icu/config.gni")
 
 # 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 = [
@@ skipping 272 matching lines @@
   configs += [ ":icu_code" ]
   public_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" ]

[Nico, 2015/05/28 02:33:51]

I'm not sure if this is right. The comment refers to -Wno-header-hygiene below;
the comment is in the wrong place.

But if ICU builds without disabling extra_warnings, I suppose that's a Good
Thing :-)

[jungshik at Google, 2015/05/28 18:07:13]

builds/config/clang/BUILD.gn has the following (I guess that's the only place
where extra_warnings is defined). |extra_warnings| has '-Wheader-hygiene' and
'-Wstring-conversion'. So, the comment placement makes sense (although one has
to go look at what |extra_warnings| has to understand the comment ;-) ). 

config("extra_warnings") {
  cflags = [
    "-Wheader-hygiene",

    # Warns when a const char[] is converted to bool.
    "-Wstring-conversion",
  ]

-
-    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",
     "source/common/bmpset.cpp",
     "source/common/brkeng.cpp",
     "source/common/brkiter.cpp",
     "source/common/bytestream.cpp",
     "source/common/bytestriebuilder.cpp",
@@ skipping 245 matching lines @@
         sources = [
           "android/icudtl_dat.S",
         ]
       } else {
         assert(false, "No icu data for this platform")
       }
       defines = [ "U_HIDE_DATA_SYMBOL" ]
     }
   }
 }