Perf will core dump if --per-socket/core -a are applied for perf stat.

The root cause is that cpu_map__build_map set refcnt of evlist's cpu_map
to 1.  It should set refcnt for the newly created cpu_map, not evlist's
cpu_map.

Here is the example:

  # perf stat -e cycles --per-socket -a sleep 1

   Performance counter stats for 'system wide':

  S0       36         30,196,257      cycles
  S1       28         15,823,536      cycles

       1.001126828 seconds time elapsed

  *** Error in `./perf': corrupted double-linked list: 0x00000000021f9090 ***
  ======= Backtrace: =========
  /lib64/libc.so.6[0x3002e7bbe7]
  /lib64/libc.so.6[0x3002e7d2b5]
  ./perf(perf_evsel__delete+0x28)[0x485bdd]
  ./perf[0x4800e8]
  ./perf(perf_evlist__delete+0x5e)[0x482cd5]
  ./perf(cmd_stat+0xf25)[0x432328]
  ./perf[0x4768e0]
  ./perf[0x476ad6]
  ./perf[0x476b41]
  ./perf(main+0x1d0)[0x476db2]
  /lib64/libc.so.6(__libc_start_main+0xf5)[0x3002e21b45]
  ./perf[0x4202c5]
Signed-off-by: Kan Liang <kan.liang@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Link: http://lkml.kernel.org/r/1444388363-35936-1-git-send-email-kan.liang@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>