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/x509_time_test.c b/test/x509_time_test.c
index 5983bdf..d672a9a 100644
--- a/test/x509_time_test.c
+++ b/test/x509_time_test.c
@@ -482,7 +482,7 @@
     return ret;
 }
 
-int setup_tests()
+int setup_tests(void)
 {
     ADD_TEST(test_x509_cmp_time_current);
     ADD_ALL_TESTS(test_x509_cmp_time, OSSL_NELEM(x509_cmp_tests));