Fix compilation with Xcode version of clang.

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")
 if (is_ios) {
   import("//build/config/ios/ios_sdk.gni")
 }
 import("//build/config/mac/mac_sdk.gni")
 import("//build/config/mac/symbols.gni")
 
 assert(host_os == "mac")
 
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/goma.gni")
 import("//build/toolchain/toolchain.gni")
 import("//build/toolchain/concurrent_links.gni")
 
-if (use_goma) {
-  assert(cc_wrapper == "", "Goma and cc_wrapper can't be used together.")
-  compiler_prefix = "$goma_dir/gomacc "
-} else if (cc_wrapper != "") {
-  compiler_prefix = cc_wrapper + " "
-} else {
-  compiler_prefix = ""
-}
-
-if (!use_xcode_clang) {
-  compiler_prefix =
-      compiler_prefix + rebase_path("$clang_base_path/bin/", root_build_dir)
-}
-
 declare_args() {
   # Reduce the number of tasks using the copy_bundle_data and compile_xcassets
   # tools as they can cause lots of I/O contention when invoking ninja with a
   # large number of parallel jobs (e.g. when using distributed build like goma).
   bundle_pool_depth = -1
 }
 
 if (current_toolchain == default_toolchain) {
   pool("bundle_pool") {
     if (bundle_pool_depth == -1) {
@@ skipping 31 matching lines @@
 # build args in this definition.
 template("mac_toolchain") {
   toolchain(target_name) {
     assert(defined(invoker.toolchain_cpu),
            "mac_toolchain() must specify a \"toolchain_cpu\"")
     assert(defined(invoker.toolchain_os),
            "mac_toolchain() must specify a \"toolchain_os\"")
 
     # concurrent_links is picked up from the declare_arg().
 
-    cc = "${compiler_prefix}clang"
-    cxx = "${compiler_prefix}clang++"
+    if (use_goma) {
+      assert(cc_wrapper == "", "Goma and cc_wrapper can't be used together.")
+      _compiler_prefix = "$goma_dir/gomacc "
+    } else if (cc_wrapper != "") {
+      _compiler_prefix = cc_wrapper + " "
+    } else {
+      _compiler_prefix = ""
+    }
+
+    if (invoker.toolchain_os != "ios" || !use_xcode_clang) {
+      _compiler_prefix += rebase_path("$clang_base_path/bin/", root_build_dir)
+    }
+
+    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 (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.
@@ skipping 315 matching lines @@
   mac_toolchain("ios_clang_x86") {
     toolchain_cpu = "x86"
     toolchain_os = "ios"
   }
 
   mac_toolchain("ios_clang_x64") {
     toolchain_cpu = "x64"
     toolchain_os = "ios"
   }
 }