perf script: Don't disable use_callchain if input is pipe

Because perf data from pipe do not have a header with evsel attr, we
should not check that and disable symbol_conf.use_callchain. Otherwise,
perf script won't show callchains even if the data stream contains
callchain.

Before:
$ perf record -g -o - uname |perf script
Linux
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.000 MB - ]
uname 1828 182630.186578: 250000 cpu-clock: ..b9499 setup_arg_pages
uname 1828 182630.186850: 250000 cpu-clock: ..83b20 ___might_sleep
uname 1828 182630.187153: 250000 cpu-clock: ..4b6be file_map_prot_ch
...

After:
$ perf record -g -o - uname |perf script
Linux
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.000 MB - ]
uname 1833 182675.927099: 250000 cpu-clock:
ba5520 _raw_spin_lock+0xfe200040 ([kernel.kallsyms])
389dd4 expand_downwards+0xfe200154 ([kernel.kallsyms])
389f34 expand_stack+0xfe200024 ([kernel.kallsyms])
3b957e setup_arg_pages+0xfe20019e ([kernel.kallsyms])
40c80f load_elf_binary+0xfe20042f ([kernel.kallsyms])
...

Signed-off-by: He Kuang <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Wang Nan <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-script.c

···
 
 	if (!no_callchain) {
 		bool use_callchain = false;
+		bool not_pipe = false;
 
 		evlist__for_each_entry(session->evlist, evsel) {
+			not_pipe = true;
 			if (evsel->attr.sample_type & PERF_SAMPLE_CALLCHAIN) {
 				use_callchain = true;
 				break;
 			}
 		}
-		if (!use_callchain)
+		if (not_pipe && !use_callchain)
 			symbol_conf.use_callchain = false;
 	}