Detect accept4() on various platforms for versions

src/config.h

@@ -9,6 +9,8 @@
 #ifndef __CONFIG_H
 #define __CONFIG_H
 
+#include <sys/param.h>
+
 #ifdef __APPLE__
 #include <fcntl.h> // for fcntl(fd, F_FULLFSYNC)
 #include <AvailabilityMacros.h>
@@ -75,7 +77,9 @@
 #endif
 
 /* Test for accept4() */
-#if defined(__linux__) || defined(OpenBSD5_7) || \
+#if defined(__linux__) || \
+    defined(OpenBSD5_7) || \
+    __DragonFly_version >= 400305 || \
     (__FreeBSD__ >= 10 || __FreeBSD_version >= 1000000) || \
     (defined(NetBSD8_0) || __NetBSD_Version__ >= 800000000)
 #define HAVE_ACCEPT4 1