[iOS] Fix build always considered dirty.

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 74 matching lines @@
     # concurrent_links is picked up from the declare_arg().
 
     cc = "${compiler_prefix}clang"
     cxx = "${compiler_prefix}clang++"
     ld = cxx
 
     linker_driver =
         "TOOL_VERSION=${tool_versions.linker_driver} " +
         rebase_path("//build/toolchain/mac/linker_driver.py", root_build_dir)
 
-    if (is_ios && additional_toolchains != []) {
+    if (invoker.toolchain_os == "ios" && additional_toolchains != []) {
       # For a fat build, the generation of dSYM needs to be performed after the
       # generation of the fat binaries using "lipo". So disable the generation
       # of the dSYM for intermediate architecture specific binaries.
       _enable_dsyms = false
       _save_unstripped_output = false
     } else {
       _enable_dsyms = enable_dsyms
       _save_unstripped_output = save_unstripped_output
     }
 
     # Make these apply to all tools below.
     lib_switch = "-l"
     lib_dir_switch = "-L"
 
     # Object files go in this directory. Use label_name instead of
     # target_output_name since labels will generally have no spaces and will be
     # unique in the directory.
     object_subdir = "{{target_out_dir}}/{{label_name}}"
 
     # If dSYMs are enabled, this flag will be added to the link tools.
     if (_enable_dsyms) {
-      dsym_switch = " -Wcrl,dsym," + rebase_path(root_out_dir) + " "
+      dsym_switch = " -Wcrl,dsym,{{root_out_dir}} "
       _dsym_output =
           "{{root_out_dir}}/{{target_output_name}}{{output_extension}}.dSYM/"
     } else {
       dsym_switch = ""
     }
 
     if (_save_unstripped_output) {
       _unstripped_output = "{{root_out_dir}}/{{target_output_name}}{{output_extension}}.unstripped"
     }
 
@@ skipping 284 matching lines @@
 
 mac_toolchain("ios_clang_x86") {
   toolchain_cpu = "x86"
   toolchain_os = "ios"
 }
 
 mac_toolchain("ios_clang_x64") {
   toolchain_cpu = "x64"
   toolchain_os = "ios"
 }