Without the change the build against c23 compiler (like `gcc-15`) fails as:
libburn> test/poll.c: In function 'main':
libburn> test/poll.c:67:27: error: assignment to '__sighandler_t' {aka 'void (*)(int)'} from incompatible pointer type 'void (*)(void)' []
libburn> 67 | newact.sa_handler = catch_int;
libburn> | ^