x11/lavalauncher: unbreak build with clang 15

../src/output.c:43:18: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
static void noop () {}

^
 void

../src/seat.c:48:18: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
static void noop () {}

^
 void

Reported by: pkg-fallout