perf tools: Do not put a variable sized type not at the end of a struct

As this is a GNU extension and while harmless in this case, we can do
the same thing in a more clearer way by using an existing thread_map
constructor.

With this we avoid this while compiling with clang:

util/parse-events.c:2024:21: error: field 'map' with variable sized type 'struct thread_map' not at the end of a struct or class is a GNU extension
[-Werror,-Wgnu-variable-sized-type-not-at-end]
struct thread_map map;
^
1 error generated.

Cc: Adrian Hunter <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Wang Nan <[e-mail]>
Link: http://lkml.kernel.org/n/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/parse-events.c

···
 		.config = config,
 		.disabled = 1,
 	};
-	struct {
-		struct thread_map map;
-		int threads[1];
-	} tmap = {
-		.map.nr	 = 1,
-		.threads = { 0 },
-	};
+	struct thread_map *tmap = thread_map__new_by_tid(0);
+
+	if (tmap == NULL)
+		return false;
 
 	evsel = perf_evsel__new(&attr);
 	if (evsel) {
-		open_return = perf_evsel__open(evsel, NULL, &tmap.map);
+		open_return = perf_evsel__open(evsel, NULL, tmap);
 		ret = open_return >= 0;
 
 		if (open_return == -EACCES) {
···
 			 *
 			 */
 			evsel->attr.exclude_kernel = 1;
-			ret = perf_evsel__open(evsel, NULL, &tmap.map) >= 0;
+			ret = perf_evsel__open(evsel, NULL, tmap) >= 0;
 		}
 		perf_evsel__delete(evsel);
 	}