Don't assert that we only cross compile on linux

BUILD.gn

 # Copyright 2014 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/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/mips.gni")
 
 # Because standalone V8 builds are not supported, assume this is part of a
 # Chromium build.
@@ skipping 14 matching lines @@
 v8_target_arch = target_cpu
 v8_random_seed = "314159265"
 v8_toolset_for_d8 = "host"
 
 # The snapshot needs to be compiled for the host, but compiled with
 # a toolchain that matches the bit-width of the target.
 #
 # TODO(GYP): For now we only support 32-bit little-endian target builds from an
 # x64 Linux host. Eventually we need to support all of the host/target
 # configurations v8 runs on.
-if (host_cpu == "x64" &&
+if (host_cpu == "x64" && host_os == "linux" &&
     (target_cpu == "arm" || target_cpu == "mipsel" || target_cpu == "x86")) {
-  assert(host_os == "linux")
   snapshot_toolchain = "//build/toolchain/linux:clang_x86"
 } else {
   snapshot_toolchain = default_toolchain
 }
 
 ###############################################################################
 # Configurations
 #
 config("internal_config") {
   visibility = [ ":*" ]  # Only targets in this file can depend on this.
@@ skipping 1534 matching lines @@
       sources += [
         "src/d8-debug.cc",
         "$target_gen_dir/d8-js.cc",
       ]
     }
     if (v8_enable_i18n_support) {
       deps += [ "//third_party/icu" ]
     }
   }
 }