simplify external module check with macro

- a >12.000 LOC configure.ac is more than enough for everybody
- removing some 100 lines cant hurt
- the SYSTEM_LIBCDR=$SYSTEM_CDR stuff should be removed in a later step,
  by renaming them in the build

Change-Id: I5c065c5c341561258800a124b0fc1f40b3d59211

m4/libo_externals.m4

+# -*- 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/.
+#
+AC_DEFUN([libo_PUBLISH_MODULE],
+[
+    true
+    AC_SUBST([SYSTEM_$1])
+    AC_SUBST([$1_CFLAGS])
+    AC_SUBST([$1_LIBS])
+])
+
+AC_DEFUN([libo_CHECK_SYSTEM_MODULE], [
+AC_MSG_CHECKING([which $1 to use])
+if test "$with_system_$1" = "yes"; then
+    AC_MSG_RESULT([external])
+    SYSTEM_$2=YES
+    PKG_CHECK_MODULES([$2], [$3])
+else
+    AC_MSG_RESULT([internal])
+    SYSTEM_$2=NO
+    BUILD_TYPE="$BUILD_TYPE $2"
+fi
+    libo_PUBLISH_MODULE([$2])
+])
+# vim: set noet sw=4 ts=4: