Make static initialization threadsafe by default

build/config/win/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/clang/clang.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/win/visual_studio_version.gni")
 import("//build/toolchain/toolchain.gni")
 
@@ skipping 37 matching lines @@
   cflags_c = [ "/TC" ]
   cflags_cc = [ "/TP" ]
 
   cflags += [
     # Tell the compiler to crash on failures. This is undocumented
     # and unsupported but very handy.
     "/d2FastFail",
 
     # Work around crbug.com/526851, bug in VS 2015 RTM compiler.
     "/Zc:sizedDealloc-",
-
-    # Disable thread-safe statics to avoid overhead and because
-    # they are disabled on other platforms. See crbug.com/587210
-    # and -fno-threadsafe-statics.
-    "/Zc:threadSafeInit-",
   ]
 
   # Building with Clang on Windows is a work in progress and very
   # experimental. See crbug.com/82385.
   if (is_clang) {
     cflags += [ "-fmsc-version=1900" ]
 
     if (current_cpu == "x86") {
       cflags += [ "-m32" ]
     } else {
@@ skipping 346 matching lines @@
 
 # Internal stuff --------------------------------------------------------------
 
 # Config used by the MIDL template to disable warnings.
 config("midl_warnings") {
   if (is_clang) {
     # MIDL generates code like "#endif !_MIDL_USE_GUIDDEF_".
     cflags = [ "-Wno-extra-tokens" ]
   }
 }