Ensure that $(LIBLTDL) is built first

After Automake upstream commit f4e91bfc490d, the list in 'all-am:' is
reordered for this test-case (*_LTLIBRARIES is before *_PROGRAMS), which
means that linker will fail to link 'old' binary.

Previously (with automake <= 1.16), it was matter of luck -- it worked if
(a) the build was serial (-j1), and/or (b) libtool-ltdl-devel package was
installed on the box so ./configure picked the system version of libltdl.

Users should anyways use system's ltdl, so this has low priority.

diff --git a/tests/old-ltdl-iface.at b/tests/old-ltdl-iface.at
index cee29089..6f9c8001 100644
--- a/tests/old-ltdl-iface.at
+++ b/tests/old-ltdl-iface.at
@@ -62,6 +62,9 @@ MOSTLYCLEANFILES =
 include ltdl/Makefile.inc
 bin_PROGRAMS = old
 old_LDADD = -Lltdl $(LIBLTDL)
+# TODO: if --with-included-ltdl was unused this would
+# generate useless dependency.
+old_DEPENDENCIES = $(LIBLTDL)
 ]])
 
 AT_DATA([old.c],
@@ -131,7 +134,7 @@ LT_AT_CHECK_LIBTOOLIZE([--ltdl=ltdl --nonrecursive --install], 0, [expout], [exp
 
 AT_CHECK([test -f ltdl/Makefile.inc])
 
-LT_AT_BOOTSTRAP([ignore], [-I m4], [], [--add-missing], [--force])
+LT_AT_BOOTSTRAP([ignore], [-I m4], [], [--add-missing], [--force], [--with-included-ltdl])
 
 LT_AT_EXEC_CHECK([./old], 0, [[...]])