perf stat: Do not allow --for-each-cgroup without cpu

The cgroup mode should work with cpu events. Warn if --for-each-cgroup
option is used with a task target like existing -G option.

# perf stat --for-each-cgroup . sleep 1
both cgroup and no-aggregation modes only available in system-wide mode

Usage: perf stat [<options>] [<command>]

-G, --cgroup <name> monitor event in cgroup name only
-A, --no-aggr disable CPU count aggregation
-a, --all-cpus system-wide collection from all CPUs
--for-each-cgroup <name>
expand events for each cgroup

Signed-off-by: Namhyung Kim <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-stat.c

···
 	 * --per-thread is aggregated per thread, we dont mix it with cpu mode
 	 */
 	if (((stat_config.aggr_mode != AGGR_GLOBAL &&
-	      stat_config.aggr_mode != AGGR_THREAD) || nr_cgroups) &&
+	      stat_config.aggr_mode != AGGR_THREAD) ||
+	     (nr_cgroups || stat_config.cgroup_list)) &&
 	    !target__has_cpu(&target)) {
 		fprintf(stderr, "both cgroup and no-aggregation "
 			"modes only available in system-wide mode\n");
···
 		parse_options_usage(stat_usage, stat_options, "G", 1);
 		parse_options_usage(NULL, stat_options, "A", 1);
 		parse_options_usage(NULL, stat_options, "a", 1);
+		parse_options_usage(NULL, stat_options, "for-each-cgroup", 0);
 		goto out;
 	}