Roll buildtools forward and fix GN build for it.

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/ios/ios_sdk.gni")
@@ skipping 67 matching lines @@
       depsformat = "gcc"
       description = "CXX {{output}}"
       outputs = [
         "{{target_out_dir}}/{{target_output_name}}/{{source_name_part}}.o",
       ]
     }
 
     tool("asm") {
       # For GCC we can just use the C compiler to compile assembly.
       depfile = "{{output}}.d"
-      command = "$cc -MMD -MF $depfile {{defines}} {{include_dirs}} $sysroot_flags $toolchain_flags {{cflags}} {{cflags_c}} -c {{source}} -o {{output}}"
+      command = "$cc -MMD -MF $depfile {{defines}} {{include_dirs}} $sysroot_flags $toolchain_flags {{asmflags}} -c {{source}} -o {{output}}"
       depsformat = "gcc"
       description = "ASM {{output}}"
       outputs = [
         "{{target_out_dir}}/{{target_output_name}}/{{source_name_part}}.o",
       ]
     }
 
     tool("objc") {
       depfile = "{{output}}.d"
       command = "$cxx -MMD -MF $depfile {{defines}} {{include_dirs}} $sysroot_flags $toolchain_flags {{cflags}} {{cflags_c}} {{cflags_objc}} -c {{source}} -o {{output}}"
@@ skipping 87 matching lines @@
     tool("stamp") {
       command = "touch {{output}}"
       description = "STAMP {{output}}"
     }
 
     tool("copy") {
       command = "ln -f {{source}} {{output}} 2>/dev/null || (rm -rf {{output}} && cp -af {{source}} {{output}})"
       description = "COPY {{source}} {{output}}"
     }
 
-    toolchain_args() {
+    toolchain_args = {
       current_cpu = invoker.toolchain_cpu
       current_os = invoker.toolchain_os
 
       # These values need to be passed through unchanged.
       target_os = target_os
       target_cpu = target_cpu
 
       if (defined(invoker.is_clang)) {
         is_clang = invoker.is_clang
       }
@@ skipping 45 matching lines @@
   toolchain_cpu = "i386"
   toolchain_os = "mac"
   prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
                        root_build_dir)
   cc = "${goma_prefix}$prefix/clang"
   cxx = "${goma_prefix}$prefix/clang++"
   ld = cxx
   is_clang = true
   sysroot_flags = "-isysroot $mac_sdk_path -mmacosx-version-min=$mac_sdk_min"
 }