Update from https://crrev.com/329939

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")
 if (current_cpu == "arm") {
   import("//build/config/arm.gni")
 }
 if (current_cpu == "mipsel" || current_cpu == "mips64el") {
@@ skipping 140 matching lines @@
     # Allow comparing the address of references and 'this' against 0
     # in debug builds. Technically, these can never be null in
     # well-defined C/C++ and Clang can optimize such checks away in
     # release builds, but they may be used in asserts in debug builds.
     cflags_cc += [
       "-Wno-undefined-bool-conversion",
       "-Wno-tautological-undefined-compare",
     ]
   }
 
-  if (is_clang && !is_win && !is_nacl) {
+  if (is_clang && !is_nacl) {
     # This is here so that all files get recompiled after a clang roll and
     # when turning clang on or off. (defines are passed via the command line,
     # and build system rebuild things when their commandline changes). Nothing
     # should ever read this define.
-    defines += [ "CR_CLANG_REVISION=" +
-                 exec_script("//tools/clang/scripts/posix-print-revision.py",
-                             [],
-                             "trim string") ]
+    defines +=
+        [ "CR_CLANG_REVISION=" + exec_script("//tools/clang/scripts/update.py",
+                                             [ "--print-revision" ],
+                                             "trim string") ]
   }
 
   # Mac-specific compiler flags setup.
   # ----------------------------------
   if (is_mac || is_ios) {
     # These flags are shared between the C compiler and linker.
     common_mac_flags = []
 
     # CPU architecture.
     if (current_cpu == "x64") {
@@ skipping 149 matching lines @@
       ]
     }
 
     # Omit unwind support in official builds to save space. We can use breakpad
     # for these builds.
     if (is_chrome_branded && is_official_build) {
       cflags += [
         "-fno-unwind-tables",
         "-fno-asynchronous-unwind-tables",
       ]
+      defines += [ "NO_UNWIND_TABLES" ]
     } else {
       cflags += [ "-funwind-tables" ]
     }
   }
 
   # Linux/Android common flags setup.
   # ---------------------------------
   if (is_linux || is_android) {
     cflags += [
       "-fPIC",
@@ skipping 280 matching lines @@
       # http://code.google.com/p/chromium/issues/detail?id=90453
       "-Wsign-compare",
     ]
 
     # In Chromium code, we define __STDC_foo_MACROS in order to get the
     # C99 macros on Mac and Linux.
     defines = [
       "__STDC_CONSTANT_MACROS",
       "__STDC_FORMAT_MACROS",
     ]
+
+    if (using_sanitizer) {
+      # _FORTIFY_SOURCE isn't really supported by Clang now, see
+      # http://llvm.org/bugs/show_bug.cgi?id=16821.
+      # It seems to work fine with Ubuntu 12 headers though, so use it in
+      # official builds.
+      #
+      # Non-chromium code is not guaranteed to compile cleanly with
+      # _FORTIFY_SOURCE. Also, fortified build may fail when optimizations are
+      # disabled, so only do that for Release build.
+      defines += [ "_FORTIFY_SOURCE=2" ]
+    }
   }
 }
 config("no_chromium_code") {
   cflags = []
   cflags_cc = []
   defines = []
 
   if (is_win) {
     cflags += [
       "/W3",  # Warning level 3.
@@ skipping 438 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }