Move libc++ configs and flags out of //build/config/sanitizers

build/config/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/allocator.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/dcheck_always_on.gni")
 import("//build/config/features.gni")
+import("//build/config/libc++/libc++.gni")
 import("//build/config/pch.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/ui.gni")
 import("//build/toolchain/goma.gni")
 
 declare_args() {
   # When set (the default) enables C++ iterator debugging in debug builds.
   # Iterator debugging is always off in release builds (technically, this flag
   # affects the "debug" config, which is always available but applied by
   # default only in debug builds).
@@ skipping 354 matching lines @@
       # variant for each language used in the target).
       precompiled_source = "//build/precompile.cc"
 
       # Force include the header.
       cflags = [ "/FI$precompiled_header" ]
     } else if (is_mac) {
       precompiled_source = "//build/precompile.h"
     }
   }
 }