MIPS[64]: Add support for big endian build using GN

snapshot_toolchain.gni

 # Copyright 2015 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 58 matching lines @@
     # host, unless this is a ChromeOS build, in which case the same toolchain
     # (Clang or GCC) will be used for target and host by default.
     if (is_chromeos && !is_clang) {
       _clang = ""
     } else {
       _clang = "clang_"
     }
 
     if (v8_current_cpu == "x64" || v8_current_cpu == "x86") {
       _cpus = v8_current_cpu
-    } else if (v8_current_cpu == "arm64" || v8_current_cpu == "mips64el") {
+    } else if (v8_current_cpu == "arm64" || v8_current_cpu == "mips64el" ||
+               v8_current_cpu == "mips64") {
       _cpus = "x64_v8_${v8_current_cpu}"
-    } else if (v8_current_cpu == "arm" || v8_current_cpu == "mipsel") {
+    } else if (v8_current_cpu == "arm" || v8_current_cpu == "mipsel" ||
+               v8_current_cpu == "mips") {
       _cpus = "x86_v8_${v8_current_cpu}"
     } else {
       # This branch should not be reached; leave _cpus blank so the assert
       # below will fail.
       _cpus = ""
     }
 
     if (_cpus != "") {
       v8_snapshot_toolchain = "//build/toolchain/${host_os}:${_clang}${_cpus}"
     }
   }
 }
 
 assert(v8_snapshot_toolchain != "",
        "Do not know how to build a snapshot for $current_toolchain " +
            "on $host_os $host_cpu")