POSIX dynamic loader: add more logging around launch/attach, fix breakpoint handling on entry callback.

This change adds some logging around dynamic loader handling.
It also fixes an issue where the dynamic loader entry breakpoint can end
up being re-inserted, showing the wrong (i.e. software breakpoint) instruction
at the stop location when a backtrace is displayed at program startup.

I discussed with Jim Ingham a few weeks back.  Essentially the
one-hit breakpoints need to make it back to public state handling before
the software breakpoint gets cleared.  The flow I was hitting was that
the breakpoint would get set, it would get hit, it would get cleared to
step over, then it would get reapplied, when we never wanted it reapplied.
Stops at the beginning of execution would then show backtraces with
software breakpoint instructions in it, erroneously.  This change fixes it.
There might be a more elegant way to do this, or a flow change somewhere else
to avoid, but it does fix an issue I experienced in startup breakpoint handling.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@219371 91177308-0d34-0410-b5e6-96231b3b80d8