Introduce better (debug) logging for CTU

[whisperity]

... and statistical checkers, if that will ever be a thing.

Currently, if CTU mode is running, even with --verbose debug, only the following output can be get, in generic:

[] - Starting static analysis...
[] - (a clang command)

All the actions taken, or failed, during the "CTU-collect" phase are never printed to a log, which makes tracing a lot harder. Did the CTU collector hang? Did an analysis hang? The prompt can stay there for a very long time for large projects.

[dkrupp]

in verbose mode log the unsuccessful clang -ast-emit calls, clang-func-map calls and output