Update from https://crrev.com/329939

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 ad947050cc52f88c4b1ea2e465d326ba03d22364..0e28e7da8be6dce3e5b5d93500416c894b8513cd 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -158,15 +158,15 @@ config("compiler") {
     ]
   }
 
-  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.
@@ -336,6 +336,7 @@ config("compiler") {
         "-fno-unwind-tables",
         "-fno-asynchronous-unwind-tables",
       ]
+      defines += [ "NO_UNWIND_TABLES" ]
     } else {
       cflags += [ "-funwind-tables" ]
     }
@@ -636,6 +637,18 @@ config("chromium_code") {
       "__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") {