Remove duplicate -std=gnu++11 flag for Mac gn build

build/config/compiler/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/android/config.gni")
 if (current_cpu == "arm") {
   import("//build/config/arm.gni")
 }
 if (current_cpu == "mipsel" || current_cpu == "mips64el") {
   import("//build/config/mips.gni")
@@ skipping 176 matching lines @@
       ]
     }
 
     cflags += common_mac_flags
 
     # Without this, the constructors and destructors of a C++ object inside
     # an Objective C struct won't be called, which is very bad.
     cflags_objcc = [ "-fobjc-call-cxx-cdtors" ]
 
     cflags_c += [ "-std=c99" ]
-    cflags_cc += [ "-std=gnu++11" ]
 
     ldflags += common_mac_flags
   } else if (is_posix) {
     # Non-Mac Posix compiler flags setup.
     # -----------------------------------
-    if (gcc_version >= 48) {
-      cflags_cc += [ "-std=gnu++11" ]
-    }
-
     if (enable_profiling && !is_debug) {
       # The GYP build spams this define into every compilation unit, as we do
       # here, but it only appears to be used in base and a couple other places.
       # TODO(abarth): Should we move this define closer to where it's used?
       defines += [ "ENABLE_PROFILING" ]
 
       cflags += [
         "-fno-omit-frame-pointer",
         "-g",
       ]
@@ skipping 189 matching lines @@
   if (linux_use_bundled_binutils) {
     binutils_path = rebase_path("//third_party/binutils/Linux_x64/Release/bin",
                                 root_build_dir)
     cflags += [ "-B$binutils_path" ]
   }
 
   # Clang-specific compiler flags setup.
   # ------------------------------------
   if (is_clang) {
     cflags += [ "-fcolor-diagnostics" ]
+  }
+
+  # C++11 compiler flags setup.
+  # ---------------------------
+  if (is_linux || is_android || is_nacl) {
+    # gnu++11 instead of c++11 is needed because some code uses typeof() (a
+    # GNU extension).
+    # TODO(thakis): Eventually switch this to c++11 instead,
+    # http://crbug.com/427584
     cflags_cc += [ "-std=gnu++11" ]
+  } else if (!is_win) {
+    cflags_cc += [ "-std=c++11" ]
   }
 
   # Android-specific flags setup.
   # -----------------------------
   if (is_android) {
     cflags += [
       "-ffunction-sections",
       "-funwind-tables",
       "-fno-short-enums",
     ]
@@ skipping 654 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }