+
+dnl Unfortunately, even up to libtool 2.2.6a there is no way to know
+dnl exactly which version of libltdl is present in the system, so we
+dnl just assume that it's a working version as long as we have the
+dnl library and the header files.
+dnl
+dnl Check the header files first since the system may have a
+dnl libltdl.so for runtime, but no headers, and we want to bail out as
+dnl soon as possible.
+dnl
+dnl We don't need any special variable for this though, since the user
+dnl can give the proper place to find libltdl through the standard
+dnl variables like LDFLAGS and CPPFLAGS.
+
+AC_CHECK_HEADER([ltdl.h],
+ [AC_CHECK_LIB([ltdl], [lt_dlopen], [LIBLTDL=-lltdl], [LIBLTDL=])],
+ [LIBLTDL=])
+
+AS_IF([test "x$LIBLTDL" = "x"],
+ [AC_MSG_ERROR([Unable to find libltdl.])])
+AC_SUBST([LIBLTDL])