Previously, the path of TTY is generated using snprintf with %d format.
It works with TTY 1 to 10, but fails with TTY with greater number
because the number used in the name is in base 32 instead of base 10.
Since there is no standard function to convert a number to a string with
a custom base, this commit adds a function to do it.
Fixes: https://github.com/swaywm/wlroots/issues/1854