gn: add support for clang for MIPS

build/toolchain/linux/BUILD.gn

 # Copyright 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/sysroot.gni")
 import("//build/toolchain/gcc_toolchain.gni")
 
 clang_toolchain("clang_arm") {
   toolchain_cpu = "arm"
   toolchain_os = "linux"
@@ skipping 47 matching lines @@
   readelf = "readelf"
   nm = "nm"
   ar = "ar"
   ld = cxx
 
   toolchain_cpu = "x64"
   toolchain_os = "linux"
   is_clang = false
 }
 
+clang_toolchain("clang_mipsel") {
+  toolchain_cpu = "mipsel"
+  toolchain_os = "linux"
+}
+
 gcc_toolchain("mipsel") {
   cc = "mipsel-linux-gnu-gcc"
   cxx = "mipsel-linux-gnu-g++"
   ar = "mipsel-linux-gnu-ar"
   ld = cxx
   readelf = "mipsel-linux-gnu-readelf"
   nm = "mipsel-linux-gnu-nm"
 
   toolchain_cpu = "mipsel"
   toolchain_os = "linux"
   is_clang = false
   use_ccache = false
   use_goma = false
 }