Cannot print unsigned integer constant

[markus-oberhumer]

This issue was extracted from #6829 (comment) :

test.nim(10, 8) Error: cannot convert -1 to uint64

when sizeof(int) == 8:
  var a   = 18446744073709551615'u64.uint
  const b = 18446744073709551615'u64.uint

  doAssert a is uint
  doAssert b is uint
  doAssert a == b

  echo a
  echo b # DOES NOT COMPILE

[Araq]

Now produces the correct output.