Mov Linux & Mac GN compiler flags to separate configs.

build/config/linux/BUILD.gn

 # Copyright (c) 2013 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")
 import("//build/config/features.gni")
 import("//build/config/sysroot.gni")
 import("//build/config/ui.gni")
 
+# This is included by reference in the //build/config/compiler config that
+# is applied to all targets. It is here to separate out the logic that is
+# Linux-only. This is not applied to Android, but is applied to ChromeOS.
+config("compiler") {
+  cflags = [ "-pthread" ]
+  ldflags = [ "-pthread" ]
+}
+
 # This is included by reference in the //build/config/compiler:runtime_library
 # config that is applied to all targets. It is here to separate out the logic
 # that is Linux-only. Please see that target for advice on what should go in
 # :runtime_library vs. :compiler.
 config("runtime_library") {
   # Set here because OS_CHROMEOS cannot be autodetected in build_config.h like
   # OS_LINUX and the like.
   if (is_chromeos) {
     defines = [ "OS_CHROMEOS" ]
   }
@@ skipping 113 matching lines @@
         "-Wno-unused-function",
       ]
     }
 
     pkg_config("gconf") {
       packages = [ "gconf-2.0" ]
       defines = [ "USE_GCONF" ]
     }
   }
 }