[linux] Improve link time with Chromium-bundled binutils.

build/toolchain.gypi

Index: build/toolchain.gypi
diff --git a/build/toolchain.gypi b/build/toolchain.gypi
index e0d6d7452e852bc66f8edc10e7c83e46c25a5566..dfaffd05d26540fbc89208b616eeb6a4d6561cf5 100644
--- a/build/toolchain.gypi
+++ b/build/toolchain.gypi
@@ -86,6 +86,46 @@
     # Allow to suppress the array bounds warning (default is no suppression).
     'wno_array_bounds%': '',
 
+    # Override where to find binutils
+    'binutils_dir%': '',
+
+    'conditions': [
+      ['OS=="linux" and host_arch=="x64"', {
+        'binutils_dir%': 'third_party/binutils/Linux_x64/Release/bin',
+      }],
+      ['OS=="linux" and host_arch=="ia32"', {
+        'binutils_dir%': 'third_party/binutils/Linux_ia32/Release/bin',
+      }],
+
+      # linux_use_bundled_gold: whether to use the gold linker binary checked
+      # into third_party/binutils.  Force this off via GYP_DEFINES when you
+      # are using a custom toolchain and need to control -B in ldflags.
+      # Do not use 32-bit gold on 32-bit hosts as it runs out address space
+      # for component=static_library builds.
+      ['OS=="linux" and (target_arch=="x64" or target_arch=="arm")', {
+        'linux_use_bundled_gold%': 1,
+      }, {
+        'linux_use_bundled_gold%': 0,
+      }],
+      # linux_use_bundled_binutils: whether to use the binary binutils
+      # checked into third_party/binutils.  These are not multi-arch so cannot
+      # be used except on x86 and x86-64 (the only two architectures which
+      # are currently checke in).  Force this off via GYP_DEFINES when you
+      # are using a custom toolchain and need to control -B in cflags.
+      ['OS=="linux" and (target_arch=="ia32" or target_arch=="x64")', {
+        'linux_use_bundled_binutils%': 1,
+      }, {
+        'linux_use_bundled_binutils%': 0,
+      }],
+      # linux_use_gold_flags: whether to use build flags that rely on gold.
+      # On by default for x64 Linux.
+      ['OS=="linux" and target_arch=="x64"', {
+        'linux_use_gold_flags%': 1,
+      }, {
+        'linux_use_gold_flags%': 0,
+      }],
+    ],
+
     # Link-Time Optimizations
     'use_lto%': 0,
 
@@ -797,6 +837,26 @@
           '-mx32',
         ],
       }],  # v8_target_arch=="x32"
+      ['linux_use_gold_flags==1', {
+        # Newer gccs and clangs support -fuse-ld, use the flag to force gold
+        # selection.
+        # gcc -- http://gcc.gnu.org/onlinedocs/gcc-4.8.0/gcc/Optimize-Options.html
+        'ldflags': [ '-fuse-ld=gold', ],
+      }],
+      ['linux_use_bundled_binutils==1', {
+        'cflags': [
+          '-B<!(cd <(DEPTH) && pwd -P)/<(binutils_dir)',
+        ],
+      }],
+      ['linux_use_bundled_gold==1', {
+        # Put our binutils, which contains gold in the search path. 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.
+        'ldflags': [
+          '-B<!(cd <(DEPTH) && pwd -P)/<(binutils_dir)',
+        ],
+      }],
       ['OS=="win"', {
         'defines': [
           'WIN32',
@@ -1083,6 +1143,21 @@
               }],
             ],
           }],
+          ['linux_use_gold_flags==1', {
+            'target_conditions': [
+              ['_toolset=="target"', {
+                'ldflags': [
+                  # Experimentation found that using four linking threads
+                  # saved ~20% of link time.
+                  # https://groups.google.com/a/chromium.org/group/chromium-dev/browse_thread/thread/281527606915bb36
+                  # Only apply this to the target linker, since the host
+                  # linker might not be gold, but isn't used much anyway.
+                  '-Wl,--threads',
+                  '-Wl,--thread-count=4',
+                ],
+              }],
+            ],
+          }],
         ],
       },  # DebugBaseCommon
       'Debug': {