perf tools: Disable kernel symbol demangling by default

Some Linux symbols (for example __vt_event_wait) are interpreted by the
demangler as C++ mangled names, which of course they aren't.

Disable kernel symbol demangling by default to avoid this, and allow
enabling it with a new option --demangle-kernel for those who wish it.

Reported-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1410581705-26968-1-git-send-email-avi@cloudius-systems.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index 3f95ea0..bec4b7b 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -120,6 +120,7 @@
 			annotate_src,
 			event_group,
 			demangle,
+			demangle_kernel,
 			filter_relative,
 			show_hist_headers;
 	const char	*vmlinux_name,