Fix gdbserver <library-list> and its #FIXED version="1.0"

While reimplementing <library-list/> I found from expat-2.0.1-11.fc15.x86_64:

warning: while parsing target library list (at line 1): Required attribute "version" of <library-list-svr4> not specified

I believe the same bug has to apply for existing FSF gdbserver but I do not
have any <library-list/> platform to test it (I did not try to build MinGW).

features/library-list.dtd:
<!ATTLIST library-list  version CDATA   #FIXED  "1.0">

http://www.xml.com/pub/a/98/10/guide0.html?page=3 says:

	In this case, the attribute is not required, but if it occurs, it must
	have the specified value.

Which would suggest gdbserver is right but solib-target.c is wrong.  One could
also make gdbserver explicit for the version (if those 14 bytes are not of
a concern).

gdb/ChangeLog
2015-06-10  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* solib-target.c (library_list_start_list): Do not dereference
	variable version in its initialization.  Make the VERSION check handle
	NULL.
	(library_list_attributes): Make "version" GDB_XML_AF_OPTIONAL.

gdb/gdbserver/ChangeLog
2015-06-10  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* server.c (handle_qxfer_libraries): Set `version' attribute for
	<library-list>.

1 files changed, 12 insertions, 6 deletions

diff --git a/gdb/solib-target.c b/gdb/solib-target.c
index bd8f58ad8c7..891e5729ab1 100644
--- a/gdb/solib-target.c
+++ b/gdb/solib-target.c
@@ -146,12 +146,18 @@ library_list_start_list (struct gdb_xml_parser *parser,
 			 const struct gdb_xml_element *element,
 			 void *user_data, VEC(gdb_xml_value_s) *attributes)
 {
-  char *version = xml_find_attribute (attributes, "version")->value;
+  struct gdb_xml_value *version = xml_find_attribute (attributes, "version");
 
-  if (strcmp (version, "1.0") != 0)
-    gdb_xml_error (parser,
-		   _("Library list has unsupported version \"%s\""),
-		   version);
+  /* #FIXED attribute may be omitted, Expat returns NULL in such case.  */
+  if (version)
+    {
+      const char *string = version->value;
+
+      if (strcmp (string, "1.0") != 0)
+	gdb_xml_error (parser,
+		       _("Library list has unsupported version \"%s\""),
+		       version);
+    }
 }
 
 /* Discard the constructed library list.  */
@@ -210,7 +216,7 @@ static const struct gdb_xml_element library_list_children[] = {
 };
 
 static const struct gdb_xml_attribute library_list_attributes[] = {
-  { "version", GDB_XML_AF_NONE, NULL, NULL },
+  { "version", GDB_XML_AF_OPTIONAL, NULL, NULL },
   { NULL, GDB_XML_AF_NONE, NULL, NULL }
 };