add PCH for pdfium

It's an external library, but it's a large C++ lib and it's built
using gbuild, so this helps too. Here with Clang it cuts build
time from ~2:40 to ~1:25 (and about halves the CPU user time).
Hopefully it also helps to reduce the build time for Windows gerrit builds.

Change-Id: Ieef0ea28e0fe1fd216592fca70410075d95ddc54
Reviewed-on: https://gerrit.libreoffice.org/72517
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

bin/update_pch

@@ -423,6 +423,10 @@ def filter_ignore(line, module):
             'xmlsec/*',
             'xmlsecurity/xmlsec-wrapper.h',
             ]
+    if module == 'external/pdfium':
+        ignore_list += [
+            'third_party/freetype/include/pstables.h',
+            ]
 
     for i in ignore_list:
         if line.startswith(i):

external/pdfium/Library_pdfium.mk

@@ -13,9 +13,12 @@ $(eval $(call gb_Library_use_unpacked,pdfium,pdfium))
 
 $(eval $(call gb_Library_set_warnings_not_errors,pdfium))
 
+$(eval $(call gb_Library_set_precompiled_header,pdfium,$(SRCDIR)/external/pdfium/inc/pch/precompiled_pdfium))
+
 $(eval $(call gb_Library_set_include,pdfium,\
     -I$(call gb_UnpackedTarball_get_dir,pdfium) \
     -I$(call gb_UnpackedTarball_get_dir,pdfium)/third_party \
+    -I$(call gb_UnpackedTarball_get_dir,pdfium)/third_party/agg23 \
     $$(INCLUDE) \
 ))
 

external/pdfium/inc/pch/precompiled_pdfium.cxx

+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include "precompiled_pdfium.hxx"
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */