Use strict function prototypes

Fixes clang error:
error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]

kittens/choose/unix_compat.c

@@ -19,7 +19,7 @@
 #endif
 
 int
-cpu_count() {
+cpu_count(void) {
     return sysconf(_SC_NPROCESSORS_ONLN);
 }