spin off easy stuff from Herb's windows GN CL

third_party/giflib/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("giflib") {
   public_include_dirs = [ "../externals/giflib" ]
 
+  if (is_win) {
+    include_dirs = [ "." ]
+  }
+
   sources = [
     "../externals/giflib/dgif_lib.c",
     "../externals/giflib/gif_err.c",
     "../externals/giflib/gifalloc.c",
   ]
 }