liblink: do not print pointers in debug output

liblink: do not print pointers in debug output

Pointers change from run to run, making it hard to use
the debug output to identify the reason for a changed
object file.

Change-Id: I0c954da0943092c48686afc99ecf75eba516de6a
Reviewed-on: https://go-review.googlesource.com/3352
Reviewed-by: Aram Hăvărneanu <aram@mgk.ro>
Reviewed-by: Rob Pike <r@golang.org>