perf stat: Fix crash on arm64

perf stat: Fix crash on arm64

Perf stat is crashing on arm64 hosts with the following issue:

  # make -C tools/perf DEBUG=1
  # perf stat sleep 1
  perf: util/evsel.c:2034: get_group_fd: Assertion `!(!leader->core.fd)' failed.
  [1]    1220794 IOT instruction (core dumped)  ./perf stat

The sorting function introduced by commit a745c0831c15c ("perf stat:
Sort default events/metrics") compares events based on their individual
properties. This can cause events from different groups to be
interleaved, resulting in group members appearing before their leaders
in the sorted evlist.

When the iterator opens events in list order, a group member may be
processed before its leader has been opened.

For example, CPU_CYCLES (idx=32) with leader STALL_SLOT_BACKEND (idx=37)
could be sorted before its leader, causing the crash when CPU_CYCLES
tries to get its group fd from the not-yet-opened leader.

Fix this by comparing events based on their leader's attributes instead
of their own attributes when the events are in different groups. This
ensures all members of a group share the same sort key as their leader,
keeping groups together and guaranteeing leaders are opened before their
members.

Fixes: a745c0831c15c ("perf stat: Sort default events/metrics")
Reported-by: Denis Yaroshevskiy <dyaroshev@meta.com>
Tested-by: Dmitry Ilvokhin <d@ilvokhin.com>
Tested-by: Ian Rogers <irogers@google.com>
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>