Allow building of XFA branch without XFA

samples/BUILD.gn

 # Copyright 2014 PDFium 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("../pdfium.gni")
+
 group("samples") {
   deps = [
     ":pdfium_test",
   ]
 }
 
 config("pdfium_samples_config") {
   defines = [
     "PNG_PREFIX",
     "PNGPREFIX_H",
     "PNG_USE_READ_MACROS",
   ]
+  if (pdf_enable_xfa) {
+    defines += [ "PDF_ENABLE_XFA" ]
+  }
 }
 
 executable("pdfium_test") {
   sources = [
     "image_diff_png.cc",
     "pdfium_test.cc",
   ]
   deps = [
     "//third_party/pdfium",
     "//v8:v8_libplatform",
   ]
   include_dirs = [
     "//v8",
     "//v8/include",
   ]
   configs += [ ":pdfium_samples_config" ]
 }
 
 executable("pdfium_diff") {
   sources = [
     "image_diff.cc",
     "image_diff_png.cc",
     "image_diff_png.h",
   ]
   deps = [
     "//third_party/pdfium",
   ]
   configs += [ ":pdfium_samples_config" ]
 }