perf script: Assume native_arch for pipe mode

In pipe mode, session->header.env.arch is not populated until the events
are processed. Therefore, the following command crashes:

perf record -o - | perf script

(gdb) bt

It fails when we try to compare env.arch against uts.machine:

if (!strcmp(uts.machine, session->header.env.arch) ||
(!strcmp(uts.machine, "x86_64") &&
!strcmp(session->header.env.arch, "i386")))
native_arch = true;

In pipe mode, it is tricky to find env.arch at this stage. To keep it
simple, let's just assume native_arch is always true for pipe mode.

Reported-by: David Carrillo Cisneros <[e-mail]>
Signed-off-by: Song Liu <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: [e-mail]
Cc: [e-mail] #v5.1+
Fixes: 3ab481a1cfe1 ("perf script: Support insn output for normal samples")
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-script.c

···
 		goto out_delete;
 
 	uname(&uts);
-	if (!strcmp(uts.machine, session->header.env.arch) ||
+	if (data.is_pipe ||  /* assume pipe_mode indicates native_arch */
+	    !strcmp(uts.machine, session->header.env.arch) ||
 	    (!strcmp(uts.machine, "x86_64") &&
 	     !strcmp(session->header.env.arch, "i386")))
 		native_arch = true;