Force load the Xcode arc libraries when building with llvm-build.

build/common.gypi

 # 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 4017 matching lines @@
                   'STRIP_INSTALLED_PRODUCT': 'YES',
                 },
               },
               'Debug_Base': {
                 'xcode_settings': {
                   # Remove dSYM to reduce build time.
                   'DEBUG_INFORMATION_FORMAT': 'dwarf',
                 },
               },
             },
-            'xcode_settings': {
-              # It is necessary to link with the -fobjc-arc flag to use
-              # subscripting on iOS < 6.
-              'OTHER_LDFLAGS': [
-                '-fobjc-arc',
-              ],
-            },
             'conditions': [
-              # TODO(justincohen): ninja builds don't support signing yet.
-              ['"<(GENERATOR)"!="ninja"', {
+              ['"<(GENERATOR)"=="xcode"', {
                 'xcode_settings': {
+                  # TODO(justincohen): ninja builds don't support signing yet.
                   'conditions': [
                     ['chromium_ios_signing', {
                       # iOS SDK wants everything for device signed.
                       'CODE_SIGN_IDENTITY[sdk=iphoneos*]': 'iPhone Developer',
                     }, {
                       'CODE_SIGNING_REQUIRED': 'NO',
                       'CODE_SIGN_IDENTITY[sdk=iphoneos*]': '',
                     }],
                   ],
                 },
               }],
+              ['"<(GENERATOR)"=="xcode" and clang!=1', {
+                'xcode_settings': {
+                  # It is necessary to link with the -fobjc-arc flag to use
+                  # subscripting on iOS < 6.
+                  'OTHER_LDFLAGS': [
+                    '-fobjc-arc',
+                  ],
+                },
+              }],
+              ['clang==1', {
+                'target_conditions': [
+                  ['_toolset=="target"', {
+                    'variables': {
+                      'developer_dir': '<!(xcode-select -print-path)',
+                      'arc_toolchain_path': '<(developer_dir)/Toolchains/XcodeDefault.xctoolchain/usr/lib/arc',
+                    },
+                    # It is necessary to force load libarclite from Xcode for
+                    # third_party/llvm-build because libarclite_* is only
+                    # distributed by Xcode.
+                    'conditions': [
+                      ['"<(GENERATOR)"=="ninja" and target_arch=="armv7"', {
+                        'xcode_settings': {
+                          'OTHER_LDFLAGS': [
+                            '-force_load',
+                            '<(arc_toolchain_path)/libarclite_iphoneos.a',
+                          ],
+                        },
+                      }],
+                      ['"<(GENERATOR)"=="ninja" and target_arch!="armv7"', {
+                        'xcode_settings': {
+                          'OTHER_LDFLAGS': [
+                            '-force_load',
+                            '<(arc_toolchain_path)/libarclite_iphonesimulator.a',
+                          ],
+                        },
+                      }],
+                      # Xcode sets target_arch at compile-time.
+                      ['"<(GENERATOR)"=="xcode"', {
+                        'xcode_settings': {
+                          'OTHER_LDFLAGS[arch=armv7]': [
+                            '-force_load',
+                            '<(arc_toolchain_path)/libarclite_iphoneos.a',
+                          ],
+                          'OTHER_LDFLAGS[arch=i386]': [
+                            '-force_load',
+                            '<(arc_toolchain_path)/libarclite_iphonesimulator.a',
+                          ],
+                        },
+                      }],
+                    ],
+                  }],
+                ],
+              }],
             ],
           }],
         ],  # target_conditions
       },  # target_defaults
     }],  # OS=="ios"
     ['OS=="win"', {
       'target_defaults': {
         'defines': [
           '_WIN32_WINNT=0x0602',
           'WINVER=0x0602',
@@ skipping 370 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }