Clean up GN template code.

build/toolchain/mac/BUILD.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.
 
 # TODO(brettw) Use "gcc_toolchain.gni" like the Linux toolchains. This requires
 # some enhancements since the commands on Mac are slightly different than on
 # Linux.
 
 import("../goma.gni")
 import("//build/config/clang/clang.gni")
@@ skipping 40 matching lines @@
 tool_versions =
     exec_script("get_tool_mtime.py",
                 rebase_path([
                               "//build/toolchain/mac/compile_xcassets.py",
                               "//build/toolchain/mac/filter_libtool.py",
                               "//build/toolchain/mac/linker_driver.py",
                             ],
                             root_build_dir),
                 "trim scope")
 
-# Work around for unused variable warning in template https://crbug.com/395883.
-assert(tool_versions != "")
-
 # Shared toolchain definition. Invocations should set current_os to set the
 # build args in this definition.
 template("mac_toolchain") {
   toolchain(target_name) {
     # When invoking this toolchain not as the default one, these args will be
     # passed to the build. They are ignored when this is the default toolchain.
     assert(defined(invoker.toolchain_args),
            "Toolchains must declare toolchain_args")
     toolchain_args = {
       # Populate toolchain args from the invoker.
@@ skipping 376 matching lines @@
     }
   }
 
   mac_toolchain("ios_clang_x64") {
     toolchain_args = {
       current_cpu = "x64"
       current_os = "ios"
     }
   }
 }