Add URBI_WITH_LTDL. Detect the presence of ltdl.
Add URBI_WITH_LTDL. Detect the presence of ltdl.

	* build-aux/urbi-with-ltdl.m4: Here.

aldebaran/libport,aldebaran/libport,aldebaran/libport,aldebaran/libport,aldebaran/libport