[PATCH] Fix dwarf2_string_attr for -gsplit-dwarf

["Leszek Swirski via gdb-patches" <gdb-patches@sourceware.org>]

The dwarf2_string_attr did not allow DW_FORM_GNU_str_index as a form for
string types. This manifested as null strings in the namespace_name
lookup (replaced with "(anonymous namespace)") when debugging
Fission-compiled code.

gdb/ChangeLog:

	* dwarf2read.c (dwarf2_string_attr): Allow DW_FORM_GNU_strp_alt.

(cherry picked from commits 16eb6b2db49e6cf2fdca56efd37689fcc170cd37 and
b33404388e5bbd8a1fddfde73cd4593ae2b557e8)
---
 gdb/ChangeLog    | 4 ++++
 gdb/dwarf2read.c | 4 +++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index b77435ce7a..bfa2359a35 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,7 @@
+2017-10-25  Leszek Swirski  <leszeks@google.com>
+
+	* dwarf2read.c (dwarf2_string_attr): Allow DW_FORM_GNU_str_index.
+
 2017-10-16  Walfred Tedeschi  <walfred.tedeschi@intel.com>
 
 	* features/Makefile (i386-avx-mpx-avx512-pku.dat): Add backslash 
diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 8503e6171c..93ec587787 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -17577,7 +17577,9 @@ dwarf2_string_attr (struct die_info *die, unsigned int name, struct dwarf2_cu *c
   if (attr != NULL)
     {
       if (attr->form == DW_FORM_strp || attr->form == DW_FORM_line_strp
-	  || attr->form == DW_FORM_string || attr->form == DW_FORM_GNU_strp_alt)
+	  || attr->form == DW_FORM_string
+	  || attr->form == DW_FORM_GNU_str_index
+	  || attr->form == DW_FORM_GNU_strp_alt)
 	str = DW_STRING (attr);
       else
         complaint (&symfile_complaints,
-- 
2.15.0.rc2.357.g7e34df9404-goog