perf script: Implement option for system-wide profiling

The option is documented in man perf-script but was not yet implemented:

-a
Force system-wide collection. Scripts run without a
<command> normally use -a by default, while scripts run
with a <command> normally don't - this option allows the
latter to be run in system-wide mode.

As with perf record you now can profile in system-wide mode for the
runtime of a given command, e.g.:

# perf script -a syscall-counts sleep 2

Cc: Ingo Molnar <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Robert Richter <[e-mail]>
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-script.c

···
 extern const struct option	record_options[];
 static bool			no_callchain;
 static bool			show_full_info;
+static bool			system_wide;
 static const char		*cpu_list;
 static DECLARE_BITMAP(cpu_bitmap, MAX_NR_CPUS);
 
···
 	OPT_CALLBACK('f', "fields", NULL, "str",
 		     "comma separated output fields prepend with 'type:'. Valid types: hw,sw,trace,raw. Fields: comm,tid,pid,time,cpu,event,trace,ip,sym,dso,addr",
 		     parse_output_fields),
+	OPT_BOOLEAN('a', "all-cpus", &system_wide,
+		     "system-wide collection from all CPUs"),
 	OPT_STRING('C', "cpu", &cpu_list, "cpu", "list of cpus to profile"),
 	OPT_STRING('c', "comms", &symbol_conf.comm_list_str, "comm[,comm...]",
 		   "only display events for these comms"),
···
 	struct perf_session *session;
 	char *script_path = NULL;
 	const char **__argv;
-	bool system_wide;
 	int i, j, err;
 
 	setup_scripting();
···
 		}
 
 		if (!pid) {
-			system_wide = true;
 			j = 0;
 
 			dup2(live_pipe[1], 1);
 			close(live_pipe[0]);
 
-			if (!is_top_script(argv[0]))
+			if (is_top_script(argv[0])) {
+				system_wide = true;
+			} else if (!system_wide) {
 				system_wide = !have_cmd(argc - rep_args,
 							&argv[rep_args]);
+			}
 
 			__argv = malloc((argc + 6) * sizeof(const char *));
 			if (!__argv)
···
 		script_path = rep_script_path;
 
 	if (script_path) {
-		system_wide = false;
 		j = 0;
 
-		if (rec_script_path)
+		if (!rec_script_path)
+			system_wide = false;
+		else if (!system_wide)
 			system_wide = !have_cmd(argc - 1, &argv[1]);
 
 		__argv = malloc((argc + 2) * sizeof(const char *));