Use void in all function definitions that do not take any arguments

Reviewed-by: Rich Salz <rsalz@openssl.org>
GH: #6208

ssl/pqueue.c

diff --git a/ssl/pqueue.c b/ssl/pqueue.c
index 29804ec..548a7a4 100644
--- a/ssl/pqueue.c
+++ b/ssl/pqueue.c
@@ -35,7 +35,7 @@
     OPENSSL_free(item);
 }
 
-pqueue *pqueue_new()
+pqueue *pqueue_new(void)
 {
     pqueue *pq = OPENSSL_zalloc(sizeof(*pq));