+ optimization in tcg8086.a_op_const_reg and .a_op_const_ref for 32-bit OP_ADD
  and OP_SUB when the low 16 bits of the const are 0



git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@25704 3ad0048d-3df7-0310-abae-a5850022a9f2