Move libcpp_is_static into //build/config/c++ [buildtools changes]

third_party/libc++/BUILD.gn

 # Copyright 2015 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/c++/c++.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/toolchain.gni")
 
-# Sanitizer builds need to override operator new, operator delete, and
-# some exception handling symbols, so libc++ must be a shared library
-# to prevent duplicate symbol errors when linking.
-libcpp_is_static = !is_component_build && !using_sanitizer
-
 # Used by libc++ and libc++abi.
 config("config") {
   defines = [ "LIBCXX_BUILDING_LIBCXXABI" ]
   if (libcpp_is_static) {
     # Don't leak any symbols on a static build.
     defines += [
       "_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS",
       "_LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS",
 
       # This resets the visibility to default only for the various
@@ skipping 66 matching lines @@
     "//build/config/compiler:no_chromium_code",
     "//build/config/compiler:rtti",
     "//build/config/sanitizers:sanitizer_options_link_helper",
   ]
   defines = [ "_LIBCPP_BUILDING_LIBRARY" ]
 
   deps = [
     "//buildtools/third_party/libc++abi",
   ]
 }