Fix inadverent change in Sql_alloc

For placement new, throw() exception specification was removed by
accident in 8fe04a3d , making  debug
tests, that simulate out-of-memory situations, fail (e.g filesort_debug)

sql/sql_alloc.h

@@ -37,7 +37,7 @@ class Sql_alloc
   }
   static void *operator new[](size_t size, MEM_ROOT *mem_root) throw ()
   { return alloc_root(mem_root, size); }
-  static void *operator new(size_t size, MEM_ROOT *mem_root)
+  static void *operator new(size_t size, MEM_ROOT *mem_root) throw()
   { return alloc_root(mem_root, size); }
   static void operator delete(void *ptr, size_t size) { TRASH(ptr, size); }
   static void operator delete(void *, MEM_ROOT *){}