perf trace: Don't print zeroed args

This way we make the output more compact.

If somebody complain (and provide a sane reason why we would like to see
zeroes) we can make it an optional, ~/.perfconfig configurable knob.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
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-myqozw43hk8z2r5hsupzdk82@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-trace.c

@@ -818,6 +818,9 @@ static size_t syscall__scnprintf_args(struct syscall *sc, char *bf, size_t size,
 			if (arg.mask & bit)
 				continue;
 
+			if (args[arg.idx] == 0)
+				continue;
+
 			printed += scnprintf(bf + printed, size - printed,
 					     "%s%s: ", printed ? ", " : "", field->name);
 			if (sc->arg_scnprintf && sc->arg_scnprintf[arg.idx]) {