perf top: Set target.system_wide

Check if neither of --pid, --tid or --uid was specified and if so, set
system_wide appropriately.

Namhyung's patch would make using any of the above target specifiers
emit a warning in perf_target__validate, since it would see
target.system_wide set and one of the others as well.

So set system_wide after validation.
Suggested-by: NDavid Ahern <dsahern@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-6e4zrji1uw0rinfyoitl0wi4@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-top.c

@@ -1258,6 +1258,10 @@ int cmd_top(int argc, const char **argv, const char *prefix __used)
 	if (top.target.uid_str != NULL && top.target.uid == UINT_MAX - 1)
 		goto out_delete_evlist;
 
+	if (top.target.tid == 0 && top.target.pid == 0 &&
+	    top.target.uid_str == NULL)
+		top.target.system_wide = true;
+
 	if (perf_evlist__create_maps(top.evlist, &top.target) < 0)
 		usage_with_options(top_usage, options);