assert (! "unexpected dynamic reloc type");

[Roland McGrath]

A friend is hitting the `assert (! "unexpected dynamic reloc type");'
with some glibc and some weird shared objects on some platform (arm),
and he suggested that the message would be more helpful if it mentioned
the offending type code, or the name of the offending shared object, or both.

Since the total set of reloc types on some of the newer platforms does seem
to be a bit of a moving target, it seems like a good plan to expect this to
be hit once in a while and make it a bit easier to figure out what's going
on when it does. 

Any objections to changing this to use _dl_signal_error with
a suitably composed message?