Fix compiler warnings

[kojix2]

• There were many "old-style function definition" warnings during compilation.

  • Updated 12 files to use modern function definitions.
  • In qsort.c, I changed the swapfunc function style.
  • Now, there are no compiler warnings.

• Tested on:

  • gcc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
  • ruby 3.4.3 (2025-04-14 revision d0b7e5b6a0) +PRISM [x86_64-linux]

Thank you.