posix: Pass -Werror to the compiler driver for link invocations as well.

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/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
+import("//build/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
 import("//build_overrides/build.gni")
 
 if (current_cpu == "arm" || current_cpu == "arm64") {
   import("//build/config/arm.gni")
 }
 if (current_cpu == "mipsel" || current_cpu == "mips64el") {
   import("//build/config/mips.gni")
 }
@@ skipping 1030 matching lines @@
 # Toggles between higher and lower warnings for code that is (or isn't)
 # part of Chromium.
 
 config("chromium_code") {
   if (is_win) {
     cflags = [ "/W4" ]  # Warning level 4.
   } else {
     cflags = [ "-Wall" ]
     if (treat_warnings_as_errors) {
       cflags += [ "-Werror" ]
+
+      # The compiler driver can sometimes (rarely) emit warnings before calling
+      # the actual linker.  Make sure these warnings are treated as errors as
+      # well.
+      # TODO(thakis): Enable this in use_custom_libcxx (asan) builds.
+      # TODO(thakis): Enable this in chromecast builds.
+      if (!use_custom_libcxx && !is_chromecast) {
+        ldflags = [ "-Werror" ]
+      }
     }
     if (is_clang) {
       # Enable -Wextra for chromium_code when we control the compiler.
       cflags += [ "-Wextra" ]
     }
 
     # In Chromium code, we define __STDC_foo_MACROS in order to get the
     # C99 macros on Mac and Linux.
     defines = [
       "__STDC_CONSTANT_MACROS",
@@ skipping 36 matching lines @@
     ]
     defines += [
       "_CRT_NONSTDC_NO_WARNINGS",
       "_CRT_NONSTDC_NO_DEPRECATE",
     ]
   } else {
     # GCC may emit unsuppressible warnings so don't add -Werror for no chromium
     # code. crbug.com/589724
     if (treat_warnings_as_errors && is_clang) {
       cflags += [ "-Werror" ]
+
+      # TODO(thakis): Enable this in use_custom_libcxx (asan) builds.
+      # TODO(thakis): Enable this in chromecast builds.
+      if (!use_custom_libcxx && !is_chromecast) {
+        ldflags = [ "-Werror" ]
+      }
     }
     if (is_clang && !is_nacl) {
       # TODO(thakis): Remove !is_nacl once
       # https://codereview.webrtc.org/1552863002/ made its way into chromium.
       cflags += [ "-Wall" ]
     }
   }
 
   if (is_clang) {
     cflags += [
@@ skipping 486 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
   }
 }