spin off easy stuff from Herb's windows GN CL

third_party/expat/BUILD.gn

 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 declare_args() {
 }
 
 import("../third_party.gni")
 
 third_party("expat") {
-  public_include_dirs = [ "../externals/expat" ]
+  public_include_dirs = [ "../externals/expat/lib" ]
 
   defines = [ "HAVE_MEMMOVE" ]
 
   sources = [
     "../externals/expat/lib/xmlparse.c",
     "../externals/expat/lib/xmlrole.c",
     "../externals/expat/lib/xmltok.c",
   ]
 }