lttng-trace: a new strace-alike LTTng command

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

Hi there!

I just pushed a new command line tool named `lttng-trace`, which allows tracing a
specific command and its sub-processes using the LTTng system call tracer. It focuses
on simplicity. It can be found here:

  Git website: http://git.lttng.org/?p=lttng-trace.git

Clone with:

  git clone https://git.lttng.org/lttng-trace.git

For instance, tracing the command "date" is as simple as:

  lttng-trace date

The tracing session can be optionally configured by using the usual lttng control
interfaces after this message appears:

[lttng-trace] Tracing session `date-20210218-170545` created. It can be customized using the `lttng` command.
[lttng-trace] Press <ENTER> key when ready to run the child process.

After execution of the command, the following message details how to view the trace:

[lttng-trace] Sub-process hierarchy traced successfully. View trace with `babeltrace2 /tmp/lttng-trace/date-20210218-170906`

See `lttng-trace --help` for more options.

This new command is in early alpha stage. Feedback is welcome! For instance, we are wondering whether
the default behavior should just be tracing system calls, or if some level of user-space tracing should
be enabled by default as well. Or if some new options should enable "typical" usage scenarios.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com