Bug#11766101 : 59140: LIKE CONCAT('%',@A,'%') DOESN'T MATCH WHEN @A CONTAINS LATIN1 STRING

Issue/Cause:
Issue is of memory corruption.During optimization phase, pattern to be matched in where 
clause, is prepared. This is done in Item_func_concat::val_str() function which forms the
resultant string (tmp_value) and return its pointer. In caller, Item_func_like::fix_fields, 
pattern is made to point to this string (tmp_value). In further processing, tmp_value is 
getting modified which causes pattern to have changed/wrong values.

Fix:
Allocate its own memroy location in caller, copy value of resultant string (tmp_value) 
into that and make pattern to point to that. This makes sure no further changes to 
tmp_value will affect pattern.

sql/item_cmpfunc.cc

@@ -4877,8 +4877,8 @@ bool Item_func_like::fix_fields(THD *thd, Item **ref)
       }
       if (canDoTurboBM)
       {
-        pattern     = first + 1;
         pattern_len = (int) len - 2;
+        pattern     = thd->strmake(first + 1, pattern_len);
         DBUG_PRINT("info", ("Initializing pattern: '%s'", first));
         int *suff = (int*) thd->alloc((int) (sizeof(int)*
                                       ((pattern_len + 1)*2+