Fix Wvarargs warning in XFA error code.

BUILD.gn

 # Copyright 2016 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.
 
 import("//build_overrides/v8.gni")
 import("//testing/test.gni")
 import("pdfium.gni")
 
 config("pdfium_config") {
   cflags = []
@@ skipping 1406 matching lines @@
       "xfa/fxfa/app/xfa_ffwidgetacc.h",
       "xfa/fxfa/app/xfa_ffwidgethandler.cpp",
       "xfa/fxfa/app/xfa_fontmgr.cpp",
       "xfa/fxfa/app/xfa_fwladapter.cpp",
       "xfa/fxfa/app/xfa_fwladapter.h",
       "xfa/fxfa/app/xfa_fwltheme.cpp",
       "xfa/fxfa/app/xfa_fwltheme.h",
       "xfa/fxfa/app/xfa_rendercontext.cpp",
       "xfa/fxfa/app/xfa_textlayout.cpp",
       "xfa/fxfa/app/xfa_textlayout.h",
-      "xfa/fxfa/fm2js/xfa_error.cpp",
       "xfa/fxfa/fm2js/xfa_error.h",
       "xfa/fxfa/fm2js/xfa_expression.cpp",
       "xfa/fxfa/fm2js/xfa_expression.h",
       "xfa/fxfa/fm2js/xfa_fm2jsapi.cpp",
       "xfa/fxfa/fm2js/xfa_fm2jsapi.h",
       "xfa/fxfa/fm2js/xfa_fm2jscontext.cpp",
       "xfa/fxfa/fm2js/xfa_fm2jscontext.h",
       "xfa/fxfa/fm2js/xfa_fmparse.cpp",
       "xfa/fxfa/fm2js/xfa_fmparse.h",
       "xfa/fxfa/fm2js/xfa_lexer.cpp",
@@ skipping 274 matching lines @@
 }
 
 if (pdf_is_standalone) {
   source_set("samples") {
     testonly = true
     deps = [
       "//samples",
     ]
   }
 }