Add a way to track all dlsym calls (contd.)

The followup for 4742abdc

Changes in this file got lost in the process of cherry-picking
the change across repositories.

Bug: http://b/29458203
Test: flash, set debug.ld.all to dlsym and check
      if there are messages in logcat

Change-Id: I4613908e46e75c5d9ec66396767f10fc6d3e9777