Add fatal_linker_warnings flag for GN builds

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")
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 63 matching lines @@
   # explore favoring size over speed in this case as well.
   optimize_for_size = is_android || is_ios
 
   # If this is set to true, or if LLVM_FORCE_HEAD_REVISION is set to 1
   # in the environment, we use the revision in the llvm repo to determine
   # the CLANG_REVISION to use, instead of the version hard-coded into
   # //tools/clang/scripts/update.py. This should only be used in
   # conjunction with setting LLVM_FORCE_HEAD_REVISION in the
   # environment when `gclient runhooks` is run as well.
   llvm_force_head_revision = false
+
+  # Enable fatal linker warnings. Building Chromium with certain versions
+  # of binutils can cause linker warning.
+  # See: https://bugs.chromium.org/p/chromium/issues/detail?id=457359
+  fatal_linker_warnings = true

[Dirk Pranke, 2016/06/30 20:00:41]

We don't support building Chromium on 32-bit linux hosts any more (you need a
64-bit system to build, even if you're going to run on 32-bit targets).

So, linking to that bug isn't a good example. Are there other bugs that we can
link against? Maybe you can point to a current need for this flag?

 }
 
 if (is_clang && !is_nacl) {
   update_args = [ "--print-revision" ]
   if (llvm_force_head_revision) {
     update_args += [ "--llvm-force-head-revision" ]
   }
   clang_revision =
       exec_script("//tools/clang/scripts/update.py", update_args, "trim string")
 }
@@ skipping 102 matching lines @@
 
       # The x86 toolchain currently has problems with stack-protector.
       if (is_android && current_cpu == "x86") {
         cflags += [ "-fno-stack-protector" ]
       } else {
         cflags += [ "-fstack-protector" ]
       }
     }
 
     # Linker warnings.
-    if (!(is_chromeos && current_cpu == "arm") &&
+    if ( fatal_linker_warnings &&
+        !(is_chromeos && current_cpu == "arm") &&
         !(is_android && use_order_profiling) && !is_mac && !is_ios) {
       # TODO(jochen): Enable this on chromeos on arm. http://crbug.com/356580
       # TODO(lizeb,pasko): Fix link errors when linking with order_profiling=1
       # crbug.com/485542
       ldflags += [ "-Wl,--fatal-warnings" ]
     }
   }
 
   if (is_clang && is_debug) {
     # Allow comparing the address of references and 'this' against 0
@@ skipping 1346 matching lines @@
 
 if (is_ios || is_mac) {
   # On Mac and iOS, this enables support for ARC (automatic ref-counting).
   # See http://clang.llvm.org/docs/AutomaticReferenceCounting.html.
   config("enable_arc") {
     common_flags = [ "-fobjc-arc" ]
     cflags_objc = common_flags
     cflags_objcc = common_flags
   }
 }