- Add adaptive authentication failure delay

- Rework monotonic_now/gettime_wrapper and use clock_gettime on more platforms

includes.h

@@ -29,6 +29,11 @@
 #include "options.h"
 #include "debug.h"
 
+#if __linux__
+/* For clock_gettime */
+#define _POSIX_C_SOURCE 199309L
+#endif
+
 #include <sys/types.h>
 #include <sys/ioctl.h>
 #include <sys/param.h> /* required for BSD4_4 define */