Clang update script: support fetching pre-built CMake on Mac

tools/clang/scripts/update.sh

 #!/usr/bin/env bash
 # Copyright (c) 2012 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.
 
 # This script will check out llvm and clang into third_party/llvm and build it.
 
 # Do NOT CHANGE this if you don't know what you're doing -- see
 # https://code.google.com/p/chromium/wiki/UpdatingClang
 # Reverting problematic clang rolls is safe, though.
@@ skipping 172 matching lines @@
           tar zxf - -C "${LLVM_BUILD_TOOLS_DIR}"
         echo Done
       fi
       gcc_toolchain="${LLVM_BUILD_TOOLS_DIR}/gcc482"
     else
       # Always set gcc_toolchain; llvm-symbolizer needs the bundled libstdc++.
       gcc_toolchain="$(dirname $(dirname $(which gcc)))"
     fi
   fi
 
-  if [[ "${OS}" == "Linux" ]]; then
-    # TODO(hans): Might need to make this work on Mac eventually.
+  if [[ "${OS}" == "Linux" || "${OS}" == "Darwin" ]]; then
     if [[ $(cmake --version | grep -Eo '[0-9.]+') < "3.0" ]]; then
       # We need a newer CMake version.
       if [[ ! -e "${LLVM_BUILD_TOOLS_DIR}/cmake310" ]]; then
         echo "Downloading pre-built CMake 3.10..."
         mkdir -p "${LLVM_BUILD_TOOLS_DIR}"
-        curl --fail -L "${CDS_URL}/tools/cmake310.tgz" | \
+        curl --fail -L "${CDS_URL}/tools/cmake310_${OS}.tgz" | \
           tar zxf - -C "${LLVM_BUILD_TOOLS_DIR}"
         echo Done
       fi
       export PATH="${LLVM_BUILD_TOOLS_DIR}/cmake310/bin:${PATH}"
     fi
   fi
 
   echo "LLVM_FORCE_HEAD_REVISION was set; using r${CLANG_REVISION}"
 fi
 
@@ skipping 463 matching lines @@
 
 if [[ -n "$run_tests" ]]; then
   # Run Chrome tool tests.
   ninja -C "${LLVM_BUILD_DIR}" cr-check-all
   # Run the LLVM and Clang tests.
   ninja -C "${LLVM_BUILD_DIR}" check-all
 fi
 
 # After everything is done, log success for this revision.
 echo "${PACKAGE_VERSION}" > "${STAMP_FILE}"