Bug#52884 mysql-test-run does not work with --debug option

Server crashes on 64bit linux with 'double free or corruption'
message, on 32bit mysql-test-run silently fails on bootstrap
stage. The problem is that FreeState() is called twice
for init_settings struct in _db_end_ function.
The fix is to remove superfluous FreeState() call.
Additional fix:
fixed discrepancy of result file when
debug & valgrind options are enabled
for MTR.

dbug/dbug.c

@@ -1517,10 +1517,7 @@ void _db_end_()
   while ((discard= cs->stack))
   {
     if (discard == &init_settings)
-    {
-      FreeState (cs, discard, 0);
       break;
-    }
     cs->stack= discard->next;
     FreeState(cs, discard, 1);
   }

mysql-test/r/variables_debug.result

+SET @old_debug = @@GLOBAL.debug;
 set debug= 'T';
 select @@debug;
 @@debug
@@ -22,4 +23,5 @@ SET GLOBAL debug='';
 SELECT @@global.debug;
 @@global.debug
 
+SET GLOBAL debug=@old_debug;
 End of 5.1 tests

mysql-test/t/variables_debug.test

 --source include/have_debug.inc
 
+SET @old_debug = @@GLOBAL.debug;
+
 #
 # Bug#34678 @@debug variable's incremental mode
 #
@@ -21,5 +23,6 @@ SELECT @@global.debug;
 SET GLOBAL debug='';
 SELECT @@global.debug;
 
+SET GLOBAL debug=@old_debug;
 
 --echo End of 5.1 tests

sql/set_var.cc

@@ -4239,10 +4239,15 @@ bool sys_var_thd_dbug::check(THD *thd, set_var *var)
 
 bool sys_var_thd_dbug::update(THD *thd, set_var *var)
 {
+  char buf[256];
+  String str(buf, sizeof(buf), system_charset_info), *res;
+
+  res= var->value->val_str(&str);
+
   if (var->type == OPT_GLOBAL)
-    DBUG_SET_INITIAL(var ? var->value->str_value.c_ptr() : "");
+    DBUG_SET_INITIAL(res ? res->c_ptr() : "");
   else
-    DBUG_SET(var ? var->value->str_value.c_ptr() : "");
+    DBUG_SET(res ? res->c_ptr() : "");
 
   return 0;
 }