Enable -Werror for links in asan builds.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index e21047787530d8e140f14f11b49674af0d80d218..cde27848fd6c4515552afe887282ab78dd021bd2 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -6,7 +6,6 @@ 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/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
 import("//build_overrides/build.gni")
@@ -1083,10 +1082,7 @@ config("chromium_code") {
       # 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 in use_custom_libcxx builds, crbug.com/669072
-      if (!use_custom_libcxx) {
-        ldflags = [ "-Werror" ]
-      }
+      ldflags = [ "-Werror" ]
     }
     if (is_clang) {
       # Enable -Wextra for chromium_code when we control the compiler.
@@ -1143,11 +1139,7 @@ config("no_chromium_code") {
     # code. crbug.com/589724
     if (treat_warnings_as_errors && is_clang) {
       cflags += [ "-Werror" ]
-
-      # TODO(thakis): Enable in use_custom_libcxx builds, crbug.com/669072
-      if (!use_custom_libcxx) {
-        ldflags = [ "-Werror" ]
-      }
+      ldflags = [ "-Werror" ]
     }
     if (is_clang && !is_nacl) {
       # TODO(thakis): Remove !is_nacl once