linux: use an in-tree copy of gold by default

(Reland of r120385 with newer third_party/gold.)

Rather than forcing everyone to configure their search paths etc.
we should just make this work by default.  You can set
the gyp variable linux_use_gold_binary=0 to turn it off.

Review URL: https://chromiumcodereview.appspot.com/9316002

git-svn-id: http://src.chromium.org/svn/trunk/src/build@120424 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -376,6 +376,15 @@
         }, {
           'enable_plugin_installation%': 1,
         }],
+
+        # Set to 0 to not use third_party/gold as the linker.
+        # On by default for x64 Linux.  Off for ChromeOS as cross-compiling
+        # makes things complicated.
+        ['chromeos==0 and host_arch=="x64"', {
+          'linux_use_gold_binary%': 1,
+        }, {
+          'linux_use_gold_binary%': 0,
+        }],
       ],
     },
 
@@ -434,6 +443,7 @@
     'enable_web_intents%': '<(enable_web_intents)',
     'enable_web_intents_tag%': '<(enable_web_intents_tag)',
     'enable_plugin_installation%': '<(enable_plugin_installation)',
+    'linux_use_gold_binary%': '<(linux_use_gold_binary)',
     'use_canvas_skia_skia%': '<(use_canvas_skia_skia)',
     # Whether to build for Wayland display server
     'use_wayland%': 0,
@@ -1981,6 +1991,19 @@
             'defines': ['KEEP_SHADOW_STACKS'],
             'cflags': ['-finstrument-functions'],
           }],
+          ['linux_use_gold_binary==1', {
+            'variables': {
+              # We pass the path to gold to the compiler.  gyp leaves
+              # unspecified what the cwd is when running the compiler,
+              # so the normal gyp path-munging fails us.  This hack
+              # gets the right path.
+              'gold_path': '<(PRODUCT_DIR)/../../third_party/gold',
+            },
+            'ldflags': [
+              # Put our gold binary in the search path for the linker.
+              '-B<(gold_path)',
+            ],
+          }],
         ],
       },
     }],