Include info about the specific `unittest` in `--log-traces`.

[ta0kira]

This will be useful for situations where someone wants to know if a specific test has executed a specific line of code.

The unittest name can be retrieved from argv (not Argv), but that won't say anything about which testcase it came from. Maybe the context for the unittest can also be passed as an argument.

It might make sense to just log all of argv, after the dynamic fields. The main issue here is that there will need to be a match between the header (written in RunCompiler.hs), the binary execution (called in TestRunner.hs), and the logging (done in logging.cpp.)

[ta0kira]

This might not be all that useful. I'll reopen if I can think of a good reason to add it.