Add a target in GN that generates a last_change.h file for the SVN revision.

tools/gn/secondary/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.
 
 # Base compiler configuration.
 config("compiler") {
-  include_dirs = [ "//" ]
+  include_dirs = [ "//", root_gen_dir ]
   if (is_win) {
     cflags = [
       "/Gy",  # Enable function-level linking.
       "/GS",  # Enable buffer security checking.
       "/EHsc",  # Assume C functions can't throw exceptions and don't catch
                 # structured exceptions (only C++ ones).
     ]
   } else {
     # Common GCC compiler flags setup.
     # --------------------------------
@@ skipping 371 matching lines @@
   } else {
     cflags = [ "-g1" ]
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }