Fix build with clang 15
https://github.com/PeterHajdu/fwa/pull/2

Index: fwa.c
--- fwa.c.orig
+++ fwa.c
@@ -34,12 +34,12 @@
 #include <string.h>
 #include <time.h>
 
-void usage();
-int create_queue();
+void usage(void);
+int create_queue(void);
 size_t parse_options(int, char*[]);
 struct kevent* allocate_event_memory(size_t);
 size_t set_up_events_to_watch(int, struct kevent *, size_t, char*[]);
-void set_output_buffer();
+void set_output_buffer(void);
 void handle_events(int, struct kevent*, size_t);
 
 int main(int argc, char **argv) {
@@ -59,7 +59,7 @@ int main(int argc, char **argv) {
 	return 0;
 }
 
-void usage() {
+void usage(void) {
 	printf(
 		"usage: fwa [options] <list of files to watch>\n"
 		"\noptions:\n"
@@ -160,7 +160,7 @@ size_t set_up_events_to_watch(
 	return event_slot;
 }
 
-void set_output_buffer() {
+void set_output_buffer(void) {
   static char line_buffer[512];
   setvbuf(stdout, line_buffer, _IOLBF, sizeof(line_buffer));
 }
@@ -214,7 +214,7 @@ void report_and_cleanup_events(
 	}
 }
 
-int create_queue() {
+int create_queue(void) {
 	const int queue = kqueue();
 	if (queue < 0)
 		err(1, "Unable to create kernel queue." );