perf probe: Support comp_dir to find an absolute source path

Gcc generates DW_AT_comp_dir and stores relative source path if building kernel
without O= option. In that case, perf probe --line sometimes doesn't work
without --source option, because it tries to access relative source path.

This adds DW_AT_comp_dir support to perf probe for finding an absolute source
path when no --source option.

LKML-Reference: <4C36EBE7.3060802@hitachi.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/probe-event.h

@@ -86,6 +86,7 @@ struct line_range {
 	int			end;		/* End line number */
 	int			offset;		/* Start line offset */
 	char			*path;		/* Real path name */
+	char			*comp_dir;	/* Compile directory */
 	struct list_head	line_list;	/* Visible lines */
 };