fix: #31 negative constants

[Neptunium931]

fix: #31

movq $-1, %eax

beffor:

(program [0, 0] - [1, 0]
  (instruction [0, 0] - [0, 14]
    kind: (word [0, 0] - [0, 4])
    (ERROR [0, 5] - [0, 6]
      (ERROR [0, 5] - [0, 6]))
    (int [0, 6] - [0, 8])
    (ident [0, 10] - [0, 14]
      (reg [0, 10] - [0, 14]))))

affter:

(program [0, 0] - [1, 0]
  (instruction [0, 0] - [0, 14]
    kind: (word [0, 0] - [0, 4])
    (int [0, 5] - [0, 8])
    (ident [0, 10] - [0, 14]
      (reg [0, 10] - [0, 14]))))