Windows, compile : reenable previously disabled warning C4291

no matching operator delete found; memory will not be freed if initialization throws an exception

Added a no-op delete() for MEM_ROOT based placement-new()

sql/sql_select.h

@@ -2115,6 +2115,7 @@ public:
   */
   static void *operator new(size_t size, THD *thd) throw();
   static void operator delete(void *ptr, size_t size) { TRASH(ptr, size); }
+  static void operator delete(void *, THD *) throw(){}
 
   Virtual_tmp_table(THD *thd)
   {