[clang] Enable compilation of compiler runtime for iOS simulator.

tools/clang/scripts/update.py

 #!/usr/bin/env python
 # 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 is used to download prebuilt clang binaries.
 
 It is also used by package.py to build the prebuilt clang binaries."""
 
 import argparse
@@ skipping 634 matching lines @@
   os.chdir(COMPILER_RT_BUILD_DIR)
   # TODO(thakis): Add this once compiler-rt can build with clang-cl (see
   # above).
   #if args.bootstrap and sys.platform == 'win32':
     # The bootstrap compiler produces 64-bit binaries by default.
     #cflags += ['-m32']
     #cxxflags += ['-m32']
   compiler_rt_args = base_cmake_args + [
       '-DCMAKE_C_FLAGS=' + ' '.join(cflags),
       '-DCMAKE_CXX_FLAGS=' + ' '.join(cxxflags)]
+  if sys.platform == 'darwin':
+    compiler_rt_args += ['-DCOMPILER_RT_ENABLE_IOS=ON']
   if sys.platform != 'win32':
     compiler_rt_args += ['-DLLVM_CONFIG_PATH=' +
                          os.path.join(LLVM_BUILD_DIR, 'bin', 'llvm-config'),
                         '-DSANITIZER_MIN_OSX_VERSION="10.7"']
   # compiler-rt is part of the llvm checkout on Windows but a stand-alone
   # directory elsewhere, see the TODO above COMPILER_RT_DIR.
   RmCmakeCache('.')
   RunCommand(['cmake'] + compiler_rt_args +
              [LLVM_DIR if sys.platform == 'win32' else COMPILER_RT_DIR],
              msvc_arch='x86', env=deployment_env)
@@ skipping 196 matching lines @@
     args.force_local_build = True
     if 'OS=android' not in os.environ.get('GYP_DEFINES', ''):
       # Only build the Android ASan rt on ToT bots when targetting Android.
       args.with_android = False
 
   return UpdateClang(args)
 
 
 if __name__ == '__main__':
   sys.exit(main())