GN: mark newlib_pnacl toolchain as clang

build/toolchain/nacl/BUILD.gn

 # Copyright (c) 2014 The Native Client 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/sysroot.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/nacl_toolchain.gni")
 
 # Add the toolchain revision as a preprocessor define so that sources are
 # rebuilt when a toolchain is updated.
@@ skipping 12 matching lines @@
 pnacl_newlib_rev = revisions[1]
 
 nacl_toolchain("newlib_pnacl") {
   toolchain_package = "pnacl_newlib"
   toolchain_revision = pnacl_newlib_rev
   toolchain_cpu = "pnacl"
   toolprefix =
       rebase_path("${nacl_toolchain_dir}/${toolchain_package}/bin/pnacl-",
                   root_build_dir)
 
+  is_clang = true
   cc = toolprefix + "clang"
   cxx = toolprefix + "clang++"
   ar = toolprefix + "ar"
   ld = cxx
   executable_extension = ".pexe.debug"
 
   finalize = toolprefix + "finalize"
   nonfinal_file =
       "{{root_out_dir}}/{{target_output_name}}${executable_extension}"
   finalized_file = "{{root_out_dir}}/{{target_output_name}}.pexe"
@@ skipping 107 matching lines @@
   toolchain_tuple = "i686-nacl"
 }
 
 nacl_clang_toolchains("x64") {
   toolchain_tuple = "x86_64-nacl"
 }
 
 nacl_clang_toolchains("arm") {
   toolchain_tuple = "arm-nacl"
 }