perf jit: Fix inaccurate DWARF line table

Fix an issue where addresses in the DWARF line table are offset by -0x40
(GEN_ELF_TEXT_OFFSET). This can be seen with `objdump -S` on the ELF
files after perf inject.

Committer notes:

Ian added this in his Acked-by reply:

---
Without too much knowledge this looks good to me. The original code came
from oprofile's jit support:

https://sourceforge.net/p/oprofile/oprofile/ci/master/tree/opjitconv/debug_line.c#l325
---

Signed-off-by: Nick Gasson <[e-mail]>
Acked-by: Ian Rogers <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/genelf_debug.c

···
 	 */
 
 	/* start state of the state machine we take care of */
-	unsigned long last_vma = code_addr;
+	unsigned long last_vma = 0;
 	char const  *cur_filename = NULL;
 	unsigned long cur_file_idx = 0;
 	int last_line = 1;
···
 		ent = debug_entry_next(ent);
 	}
 	add_compilation_unit(di, buffer_ext_size(dl));
-	add_debug_line(dl, debug, nr_debug_entries, 0);
+	add_debug_line(dl, debug, nr_debug_entries, GEN_ELF_TEXT_OFFSET);
 	add_debug_abbrev(da);
 	if (0) buffer_ext_dump(da, "abbrev");