https://bugs.gentoo.org/293921

ohnobinki's attempt at convincing ltdl.m4 to permit people
to delete that special type of libtool archive which has
no use on a modern GNU/Linux system.

diff --git a/libltdl/m4/ltdl.m4 b/libltdl/m4/ltdl.m4
index 111fac1..4bedc34 100644
--- a/libltdl/m4/ltdl.m4
+++ b/libltdl/m4/ltdl.m4
@@ -282,8 +282,11 @@ AC_ARG_WITH([ltdl_lib],
                     [use the libltdl.la installed in DIR])])
 
 if test -n "$with_ltdl_lib"; then
-  if test -f "$with_ltdl_lib/libltdl.la"; then :
-  else
+  # check for the existence of "$with_ltdl_lib/libltdl.la" while
+  # allowing people to libtool archive file (which isn't useful
+  # in this case in many common platforms.)
+  with_ltdl_lib_libname=$(echo "$with_ltdl_lib"/libltdl.*) 2>/dev/null
+  if test "x$with_ltdl_lib_libname" = "x$with_ltdl_lib/libltdl.*"; then
     AC_MSG_ERROR([invalid ltdl library directory: `$with_ltdl_lib'])
   fi
 else