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

Reviewed-by: Rich Salz <rsalz@openssl.org>
GH: #6208
diff --git a/test/handshake_helper.c b/test/handshake_helper.c
index 9b781b0..fc5fcd6 100644
--- a/test/handshake_helper.c
+++ b/test/handshake_helper.c
@@ -22,7 +22,7 @@
 #include "handshake_helper.h"
 #include "testutil.h"
 
-HANDSHAKE_RESULT *HANDSHAKE_RESULT_new()
+HANDSHAKE_RESULT *HANDSHAKE_RESULT_new(void)
 {
     HANDSHAKE_RESULT *ret;