test: update midifile library to ANSI C

alsa-project/alsa-lib pull request #463 was opened from atsampson:

The `midifile` library used by the `playmidi1` program dates from 1989, and used pre-ANSI function definitions and prototypes. GCC 15 now defaults to C23 where `()` means the same as `(void)` in prototypes, which causes type mismatch errors.

Update the code to use ANSI function definitions and prototypes, so it'll compile happily as anything from ANSI C to C23. This revealed that `playmidi1`'s `do_tempo` had the wrong argument type, so correct that as well.

Fixes #452.

Request URL : https://github.com/alsa-project/alsa-lib/pull/463 Patch URL : https://github.com/alsa-project/alsa-lib/pull/463.patch Repository URL: https://github.com/alsa-project/alsa-lib