Split out eval_op_binary

Split out eval_op_binary

This splits out a new eval_op_binary helper function.  This function
can handle several different binary operations:

    case BINOP_EXP:
    case BINOP_MUL:
    case BINOP_DIV:
    case BINOP_INTDIV:
    case BINOP_REM:
    case BINOP_MOD:
    case BINOP_LSH:
    case BINOP_RSH:
    case BINOP_BITWISE_AND:
    case BINOP_BITWISE_IOR:
    case BINOP_BITWISE_XOR:

gdb/ChangeLog
2021-03-08  Tom Tromey  <tom@tromey.com>

	* eval.c (eval_op_binary): New function.
	(evaluate_subexp_standard): Use it.