Allow use of poll() on APPLE systems if first component of

uname release string is 20 or greater.
The poll() bug seems to be fixed on 20.6.0.
I don't know exactly which release fixed in, but assume that
all 20.x releases are fixed and all earlier releases are not.

main.c

@@ -122,6 +122,7 @@ main(argc, argv)
  is_tty = isatty(1);
  init_mark();
  init_cmds();
+ init_poll();
  get_term();
  init_charset();
  init_line();

os.c

@@ -36,8 +36,13 @@
 #include <values.h>
 #endif
 
-#if HAVE_POLL && !MSDOS_COMPILER && !defined(__APPLE__)
+#if defined(__APPLE__)
+#include <sys/utsname.h>
+#endif
+
+#if HAVE_POLL && !MSDOS_COMPILER
 #define USE_POLL 1
+static int use_poll = TRUE;
 #else
 #define USE_POLL 0
 #endif
@@ -78,6 +83,17 @@ extern char *ttyin_name;
 #endif /*LESSTEST*/
 
 #if USE_POLL
+ public void
+init_poll(VOID_PARAM)
+{
+#if defined(__APPLE__)
+ /* In old versions of MacOS, poll() does not work with /dev/tty. */
+ struct utsname uts;
+ if (uname(&uts) < 0 || lstrtoi(uts.release, NULL, 10) < 20)
+ use_poll = FALSE;
+#endif
+}
+
 /*
  * Check whether data is available, either from a file/pipe or from the tty.
  * Return READ_AGAIN if no data currently available, but caller should retry later.
@@ -120,7 +136,7 @@ check_poll(fd, tty)
 supports_ctrl_x(VOID_PARAM)
 {
 #if USE_POLL
- return (TRUE);
+ return (use_poll);
 #else
  return (FALSE);
 #endif /* USE_POLL */
@@ -203,7 +219,7 @@ iread(fd, buf, len)
  }
 #endif
 #if USE_POLL
- if (fd != tty)
+ if (fd != tty && use_poll)
  {
  int ret = check_poll(fd, tty);
  if (ret != 0)