Cygwin: console: Share readahead buffer within the same process.

- The cause of the problem reported in
  https://www.cygwin.com/ml/cygwin/2020-01/msg00220.html is that the
  chars input before dup() cannot be read from the new file descriptor.
  This is because the readahead buffer (rabuf) in the console is newly
  created by dup(), and does not inherit from the parent. This patch
  fixes the issue.

winsup/cygwin/fhandler.cc

@@ -44,11 +44,11 @@ void
 fhandler_base::reset (const fhandler_base *from)
 {
   pc << from->pc;
-  rabuf = NULL;
-  ralen = 0;
-  raixget = 0;
-  raixput = 0;
-  rabuflen = 0;
+  ra.rabuf = NULL;
+  ra.ralen = 0;
+  ra.raixget = 0;
+  ra.raixput = 0;
+  ra.rabuflen = 0;
   _refcnt = 0;
 }
 
@@ -66,15 +66,15 @@ int
 fhandler_base::put_readahead (char value)
 {
   char *newrabuf;
-  if (raixput < rabuflen)
+  if (raixput () < rabuflen ())
     /* Nothing to do */;
-  else if ((newrabuf = (char *) realloc (rabuf, rabuflen += 32)))
-    rabuf = newrabuf;
+  else if ((newrabuf = (char *) realloc (rabuf (), rabuflen () += 32)))
+    rabuf () = newrabuf;
   else
     return 0;
 
-  rabuf[raixput++] = value;
-  ralen++;
+  rabuf ()[raixput ()++] = value;
+  ralen ()++;
   return 1;
 }
 
@@ -82,11 +82,11 @@ int
 fhandler_base::get_readahead ()
 {
   int chret = -1;
-  if (raixget < ralen)
-    chret = ((unsigned char) rabuf[raixget++]) & 0xff;
+  if (raixget () < ralen ())
+    chret = ((unsigned char) rabuf ()[raixget ()++]) & 0xff;
   /* FIXME - not thread safe */
-  if (raixget >= ralen)
-    raixget = raixput = ralen = 0;
+  if (raixget () >= ralen ())
+    raixget () = raixput () = ralen () = 0;
   return chret;
 }
 
@@ -94,10 +94,10 @@ int
 fhandler_base::peek_readahead (int queryput)
 {
   int chret = -1;
-  if (!queryput && raixget < ralen)
-    chret = ((unsigned char) rabuf[raixget]) & 0xff;
-  else if (queryput && raixput > 0)
-    chret = ((unsigned char) rabuf[raixput - 1]) & 0xff;
+  if (!queryput && raixget () < ralen ())
+    chret = ((unsigned char) rabuf ()[raixget ()]) & 0xff;
+  else if (queryput && raixput () > 0)
+    chret = ((unsigned char) rabuf ()[raixput () - 1]) & 0xff;
   return chret;
 }
 
@@ -105,7 +105,7 @@ void
 fhandler_base::set_readahead_valid (int val, int ch)
 {
   if (!val)
-    ralen = raixget = raixput = 0;
+    ralen () = raixget () = raixput () = 0;
   if (ch != -1)
     put_readahead (ch);
 }
@@ -1092,7 +1092,7 @@ fhandler_base::lseek (off_t offset, int whence)
   if (whence != SEEK_CUR || offset != 0)
     {
       if (whence == SEEK_CUR)
-	offset -= ralen - raixget;
+	offset -= ralen () - raixget ();
       set_readahead_valid (0);
     }
 
@@ -1142,7 +1142,7 @@ fhandler_base::lseek (off_t offset, int whence)
      readahead that we have to take into account when calculating
      the actual position for the application.  */
   if (whence == SEEK_CUR)
-    res -= ralen - raixget;
+    res -= ralen () - raixget ();
 
   return res;
 }
@@ -1565,23 +1565,23 @@ fhandler_base::fhandler_base () :
   ino (0),
   _refcnt (0),
   openflags (0),
-  rabuf (NULL),
-  ralen (0),
-  raixget (0),
-  raixput (0),
-  rabuflen (0),
   unique_id (0),
   archetype (NULL),
   usecount (0)
 {
+  ra.rabuf = NULL;
+  ra.ralen = 0;
+  ra.raixget = 0;
+  ra.raixput = 0;
+  ra.rabuflen = 0;
   isclosed (false);
 }
 
 /* Normal I/O destructor */
 fhandler_base::~fhandler_base ()
 {
-  if (rabuf)
-    free (rabuf);
+  if (ra.rabuf)
+    free (ra.rabuf);
 }
 
 /**********************************************************************/