[infra] Roll clang to match the version used by Flutter

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/mac/mac_sdk.gni")
@@ skipping 193 matching lines @@
         is_clang = invoker.is_clang
       }
     }
   }
 }
 
 # Toolchain used for Mac host targets.
 mac_toolchain("clang_x64") {
   toolchain_cpu = "x64"
   toolchain_os = "mac"
-  prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
+  prefix = rebase_path("//buildtools/toolchain/clang+llvm-x86_64-darwin/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"
 }
 
 # Toolchain used for Mac host (i386) targets.
 mac_toolchain("clang_i386") {
   toolchain_cpu = "i386"
   toolchain_os = "mac"
-  prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
+  prefix = rebase_path("//buildtools/toolchain/clang+llvm-x86_64-darwin/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"
 }