Add support for building v8 on mips and mips64 using GN.

build/config/sysroot.gni

 # 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.
 
 # This header file defines the "sysroot" variable which is the absolute path
 # of the sysroot. If no sysroot applies, the variable will be an empty string.
 
 import("//build/config/chrome_build.gni")
 
 declare_args() {
   # The absolute path of the sysroot that is applied when compiling using
   # the target toolchain.
   target_sysroot = ""
 
   # The absolute path to directory containing linux sysroot images
   target_sysroot_dir = "//build/linux"
 
   use_sysroot = current_cpu != "s390x" && current_cpu != "s390" &&
-                current_cpu != "ppc64" && current_cpu != "ppc"
+                current_cpu != "ppc64" && current_cpu != "ppc" &&
+                current_cpu != "mips" && current_cpu != "mips64"
 }
 
 if (current_os == target_os && current_cpu == target_cpu &&
     target_sysroot != "") {
   sysroot = target_sysroot
 } else if (is_android) {
   import("//build/config/android/config.gni")
   if (current_cpu == "x86") {
     sysroot = "$android_ndk_root/$x86_android_sysroot_subdir"
   } else if (current_cpu == "arm") {
@@ skipping 41 matching lines @@
   }
 } else if (is_mac) {
   import("//build/config/mac/mac_sdk.gni")
   sysroot = mac_sdk_path
 } else if (is_ios) {
   import("//build/config/ios/ios_sdk.gni")
   sysroot = ios_sdk_path
 } else {
   sysroot = ""
 }