libperf: Setup initial evlist::all_cpus value

Jann Horn reported crash in perf ftrace because evlist::all_cpus isn't
initialized if there's evlist without events, which is the case for perf
ftrace.

Adding initial initialization of evlist::all_cpus from given cpus,
regardless of events in the evlist.

Fixes: 7736627b86 ("perf stat: Use affinity for closing file descriptors")
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Andi Kleen <ak@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20200110151537.153012-1-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/perf/evlist.c

@@ -164,6 +164,9 @@ void perf_evlist__set_maps(struct perf_evlist *evlist,
 		evlist->threads = perf_thread_map__get(threads);
 	}
 
+	if (!evlist->all_cpus && cpus)
+		evlist->all_cpus = perf_cpu_map__get(cpus);
+
 	perf_evlist__propagate_maps(evlist);
 }