Add a verbosity output flag to the tracer.
Add a verbosity output flag to the tracer.

This removes a bunch of stdout messages from the tracer that are
typically not helpful. They can be re-enabled with the flag
-verbose-tracer. A more specific flag is safer to avoid conflicting with
other potential "-v" flags (version, verbose, etc.).

Change-Id: Ie9af792d5643bad21a66430403ba8be8f5547eb7

rgly/LLVM-Tracer,rgly/LLVM-Tracer,rgly/LLVM-Tracer