Import selfpipe code from skalibs 1.2.5

[andersk@mit.edu: Move code to new third/libstddjb directory]

third/libstddjb/ndelay_on.c

@@ -0,0 +1,15 @@
+/* ISC license. */
+
+#include <sys/types.h>
+#include <fcntl.h>
+#include "djbunix.h"
+
+#ifndef O_NONBLOCK
+#define O_NONBLOCK O_NDELAY
+#endif
+
+int ndelay_on (int fd)
+{
+  register int got = fcntl(fd, F_GETFL) ;
+  return (got == -1) ? -1 : fcntl(fd, F_SETFL, got | O_NONBLOCK) ;
+}