Invoke DL_AFTER_LOAD if defined

Invoke DL_AFTER_LOAD if defined

This hook is useful for any arch-specific functionality that
should be done on loaded objects.  For the tile architecture,
the hook is already provided (though we switch to using the new
macro name with this commit) and implements a simulator notifier
so that the simulator can load Elf symbols to match the object
and generate better error messages for PC's.

Also, remove a spurious definition of DL_UNMAP in dl-runtime.c