GN: Fix cross ARM64 and cross MIPS builds.

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/ccache.gni")
 import("//build/toolchain/clang.gni")
 import("//build/toolchain/gcc_toolchain.gni")
 import("//build/toolchain/goma.gni")
 
@@ skipping 91 matching lines @@
   nm = "nm"
   ar = "ar"
   ld = cxx
 
   toolchain_cpu = "x64"
   toolchain_os = "linux"
   is_clang = false
 }
 
 gcc_toolchain("mipsel") {
-  cc = "${toolchain_prefix}gcc"
-  cxx = "${toolchain_prefix}g++"
+  cc = "${toolchain_prefix}gcc -EL"

[zra, 2017/01/18 03:21:33]

Please add these here instead: 
https://github.com/dart-lang/sdk/blob/master/build/config/compiler/BUILD.gn#L228

[rmacnak, 2017/01/20 22:54:47]

Done.

+  cxx = "${toolchain_prefix}g++ -EL"
   ar = "${toolchain_prefix}ar"
   ld = cxx
   readelf = "${toolchain_prefix}readelf"
   nm = "${toolchain_prefix}nm"
 
   toolchain_cpu = "${target_cpu}"
   toolchain_os = "linux"
   is_clang = is_clang
 }