perf_counter tools: Handle lost events

Make use of the new ->data_tail mechanism to tell kernel-space
about user-space draining the data stream. Emit lost events
(and display them) if they happen.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --cc tools/perf/builtin-record.c
Simple merge

diff --cc tools/perf/builtin-report.c
Simple merge