A system with a class which has an external routine with an alias
compiles fine and is correctly frozen even if only melting is
requested.  Then the Ace is changed so that the class containing the
external routine is found in a different (newly added) cluster with a
new cluster tag, but the class text is identical.  When the system is
recompiled, the compiler terminates silently after pass 6 on the new
cluster.

Discovered in Release 3.2.2.