gn: use bundled binutils via -B

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 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.
 
 import("//build/config/android/config.gni")
 if (cpu_arch == "arm") {
   import("//build/config/arm.gni")
 }
 if (is_posix) {
   import("//build/config/gcc/gcc_version.gni")
 }
 
 declare_args() {
   # Normally, Android builds are lightly optimized, even for debug builds, to
   # keep binary size down. Setting this flag to true disables such optimization
   android_full_debug = false
+
+  # 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 that are currently checked in). Turn this off when
+  # you are using a custom toolchain and need to control -B in cflags.
+  linux_use_bundled_binutils = is_linux && cpu_arch == "x64"
 }
 
 use_gold = is_linux && cpu_arch == "x64"
 
 if (!is_win) {
   # linux_use_debug_fission: whether to use split DWARF debug info
   # files. This can reduce link time significantly, but is incompatible
   # with some utilities such as icecc and ccache. Requires gold and
   # gcc >= 4.8 or clang.
   # http://gcc.gnu.org/wiki/DebugFission
-  #
-  # TODO(GYP) enable this. Currently this gives errors from objcopy, presumably
-  # because some other symbol or toolchain setting isn't correct.
-  #use_debug_fission = use_gold
-  use_debug_fission = false
+  use_debug_fission = use_gold && linux_use_bundled_binutils
 }
 
 # default_include_dirs ---------------------------------------------------------
 #
 # This is a separate config so that third_party code (which would not use the
 # source root and might have conflicting versions of some headers) can remove
 # this and specify their own include paths.
 config("default_include_dirs") {
   include_dirs = [
     "//",
@@ skipping 218 matching lines @@
       # 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.
       # TODO(raymes): Disable threading because gold is frequently
       # crashing on the bots: crbug.com/161942.
       #"-Wl,--threads",
       #"-Wl,--thread-count=4",
     ]
   }
 
+  if (linux_use_bundled_binutils) {
+    binutils_path = rebase_path("//third_party/binutils/Linux_x64/Release/bin",
+                                root_build_dir)
+    cflags += [ "-B$binutils_path" ]
+  }
+
   # Clang-specific compiler flags setup.
   # ------------------------------------
   if (is_clang) {
     cflags += [
       "-fcolor-diagnostics",
     ]
     cflags_cc += [
       "-std=gnu++11",
     ]
   }
@@ skipping 643 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }