Import selfpipe code from skalibs 1.2.5

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

third/libstddjb/fd_close.c

@@ -0,0 +1,15 @@
+/* ISC license. */
+
+#include <unistd.h>
+#include <errno.h>
+#include "djbunix.h"
+
+int fd_close (int fd)
+{
+  register unsigned int i = 0 ;
+doit:
+  if (!close(fd)) return 0 ;
+  i++ ;
+  if (errno == EINTR) goto doit ;
+  return ((errno == EBADF) && (i > 1)) ? 0 : -1 ;
+}