libbpf-tools: add klockstat

libbpf-tools: add klockstat

This is a port of BCC's klockstat.  Differences from BCC:
- can specify a lock by ksym name, using -L
- tracks whichever task had the max time for acquire and hold, outputted
when -s > 1 (otherwise it's cluttered).
- does not reset stats each interval by default.  Can request with -R.

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Usage: klockstat [-hRT] [-p PID] [-t TID] [-c FUNC] [-L LOCK] [-n NR_LOCKS]
                 [-s NR_STACKS] [-S SORT] [-d DURATION] [-i INTERVAL]

  -p, --pid=PID              Filter by process ID
  -t, --tid=TID              Filter by thread ID
  -c, --caller=FUNC          Filter by caller string prefix
  -L, --lock=LOCK            Filter by specific ksym lock name
  -n, --locks=NR_LOCKS       Number of locks to print
  -s, --stacks=NR_STACKS     Number of stack entries to print per lock
  -S, --sort=SORT            Sort by field:
                               acq_[max|total|count]
                               hld_[max|total|count]
  -d, --duration=SECONDS     Duration to trace
  -i, --interval=SECONDS     Print interval
  -R, --reset                Reset stats each interval
  -T, --timestamp            Print timestamp

  -?, --help                 Give this help list
      --usage                Give a short usage message
  -V, --version              Print program version

Mandatory or optional arguments to long options are also mandatory or optional
for any corresponding short options.

Examples:
  klockstat                     # trace system wide until ctrl-c
  klockstat -d 5                # trace for 5 seconds
  klockstat -i 5                # print stats every 5 seconds
  klockstat -p 181              # trace process 181 only
  klockstat -t 181              # trace thread 181 only
  klockstat -c pipe_            # print only for lock callers with 'pipe_'
                                # prefix
  klockstat -L cgroup_mutex     # trace the cgroup_mutex lock only
  klockstat -S acq_count        # sort lock acquired results by acquire count
  klockstat -S hld_total        # sort lock held results by total held time
  klockstat -S acq_count,hld_total  # combination of above
  klockstat -n 3                # display top 3 locks
  klockstat -s 6                # display 6 stack entries per lock

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Signed-off-by: Barret Rhoden <brho@google.com>