build internal python before trying to use meson

Change-Id: Idb27a3e6c27640528488df263b93809221b09f1a
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/193270
Tested-by: Jenkins
Reviewed-by: Andras Timar <andras.timar@collabora.com>

external/meson/ExternalProject_meson.mk

@@ -0,0 +1,16 @@
+# -*- Mode: makefile-gmake; tab-width: 4; indent-tabs-mode: t -*-
+#
+# 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/.
+#
+
+$(eval $(call gb_ExternalProject_ExternalProject,meson))
+
+ifeq ($(SYSTEM_PYTHON),)
+$(WORKDIR)/ExternalProject/meson.prepare : $(call gb_Package_get_target,python3)
+endif
+
+# vim: set noet sw=4 ts=4:

external/meson/Module_meson.mk

@@ -10,6 +10,7 @@
 $(eval $(call gb_Module_Module,meson))
 
 $(eval $(call gb_Module_add_targets,meson,\
+    ExternalProject_meson \
     UnpackedTarball_meson \
 ))