Build and install LLVM gold plugin on Linux.

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 5872 matching lines @@
       'target_defaults': {
         'target_conditions': [
           ['_toolset=="target"', {
             'cflags': [
               '-ffat-lto-objects',
             ],
           }],
         ],
       },
     }],
+    ['use_lto==1 and clang==1', {
+      'target_defaults': {
+        'target_conditions': [
+          ['_toolset=="target"', {
+            'arflags': [
+              '--plugin', '<(DEPTH)/<(make_clang_dir)/lib/LLVMgold.so',
+            ],
+          }],
+        ],
+      },
+    }],
     ['(use_lto==1 or use_lto_o2==1) and clang==0', {
       'target_defaults': {
         'target_conditions': [
           ['_toolset=="target"', {
             'ldflags': [
               '-flto=32',
             ],
           }],
         ],
       },
@@ skipping 72 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',
   },
 }