Enable cross compile to android from mac.

build/config/BUILDCONFIG.gn

 # 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.
 
 # =============================================================================
 # BUILD FLAGS
 # =============================================================================
 #
 # This block lists input arguments to the build, along with their default
 # values. GN requires listing them explicitly so it can validate input and have
@@ skipping 470 matching lines @@
 if (is_win) {
   # On windows we use the same toolchain for host and target by default.
   # TODO(dpranke): rename the toolchains to x64 and x86 to match current_cpu.
   if (current_cpu == "x64") {
     host_toolchain = "//build/toolchain/win:64"
   } else if (current_cpu == "x86") {
     host_toolchain = "//build/toolchain/win:32"
   }
   set_default_toolchain("$host_toolchain")
 } else if (is_android) {
-  # Use clang for the x86/64 Linux host builds.
-  if (host_cpu == "x86" || host_cpu == "x64") {
-    host_toolchain = "//build/toolchain/linux:clang_$host_cpu"
+  if (host_os == "linux") {
+    # Use clang for the x86/64 Linux host builds.
+    if (host_cpu == "x86" || host_cpu == "x64") {
+      host_toolchain = "//build/toolchain/linux:clang_$host_cpu"
+    } else {
+      host_toolchain = "//build/toolchain/linux:$host_cpu"
+    }
+  } else if (host_os == "mac") {
+    host_toolchain = "//build/toolchain/mac:clang_$host_cpu"
   } else {
-    host_toolchain = "//build/toolchain/linux:$host_cpu"
+    assert(false, "Unknown host for android cross compile")
   }
   set_default_toolchain("//build/toolchain/android:$current_cpu")
 } else if (is_linux) {
   if (is_clang) {
     host_toolchain = "//build/toolchain/linux:clang_$host_cpu"
     set_default_toolchain("//build/toolchain/linux:clang_$current_cpu")
   } else {
     host_toolchain = "//build/toolchain/linux:$host_cpu"
     set_default_toolchain("//build/toolchain/linux:$current_cpu")
   }
   if (is_chromeos && cros_use_custom_toolchain) {
     set_default_toolchain("//build/toolchain/cros:target")
   }
 } else if (is_mac) {
-  host_toolchain = "//build/toolchain/mac:clang"
+  host_toolchain = "//build/toolchain/mac:clang_x64"
   set_default_toolchain(host_toolchain)
 } else if (is_ios) {
-  host_toolchain = "//build/toolchain/mac:host_clang"
-  set_default_toolchain("//build/toolchain/mac:clang")
+  host_toolchain = "//build/toolchain/mac:clang_x64"
+  set_default_toolchain("//build/toolchain/mac:clang_$current_cpu")
 } else if (is_nacl) {
   # TODO(GYP): This will need to change when we get NaCl working
   # on multiple platforms, but this whole block of code (how we define
   # host_toolchain) needs to be reworked regardless to key off of host_os
   # and host_cpu rather than the is_* variables.
   host_toolchain = "//build/toolchain/linux:clang_x64"
 }
 
 # ==============================================================================
 # COMPONENT SETUP
@@ skipping 195 matching lines @@
       }
       if (defined(invoker.testonly)) {
         testonly = invoker.testonly
       }
       if (defined(invoker.visibility)) {
         visibility = invoker.visibility
       }
     }
   }
 }