Normally, the simulator is notified of absolute pathnames by the
_dl_load_hook hook. However, when a relative pathname is used, the
simulator may not know that the relative path matches a path that
it could figure out in the file system that it has access to.
Instead we provide a simplified version of the realpath function
so we can pass a plausible absolute pathname to the simulator.
Since we're now doing more work at object load time, we also add
a guard so we do no work at all if we're not running on the simulator.
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
