Make requested console reports work

cf https://cygwin.com/ml/cygwin-patches/2012-q3/msg00019.html

This enables the following ESC sequences:
ESC[c sends primary device attributes
ESC[>c sends secondary device attributes
ESC[6n sends cursor position report

    * fhandler.h (class dev_console): Add console read-ahead buffer.
    (class fhandler_console): Add peek function for it (for select).
    * fhandler_console.cc (fhandler_console::setup): Init buffer.
    (fhandler_console::read): Check console read-aheader buffer.
    (fhandler_console::char_command): Put responses to terminal
    requests (device status and cursor position reports) into
    common console buffer (shared between CONOUT/CONIN)
    instead of fhandler buffer (separated).
    * select.cc (peek_console): Check console read-ahead buffer.

winsup/cygwin/fhandler.h

@@ -1352,6 +1352,8 @@ class dev_console
   bool ext_mouse_mode15;
   bool use_focus;
   bool raw_win32_keyboard_mode;
+  char cons_rabuf[40];  // cannot get longer than char buf[40] in char_command
+  char *cons_rapoi;
 
   inline UINT get_console_cp ();
   DWORD con_to_str (char *d, int dlen, WCHAR w);
@@ -1449,6 +1451,10 @@ private:
   int init (HANDLE, DWORD, mode_t);
   bool mouse_aware (MOUSE_EVENT_RECORD& mouse_event);
   bool focus_aware () {return shared_console_info->con.use_focus;}
+  bool get_cons_readahead_valid ()
+  {
+    return shared_console_info->con.cons_rapoi != NULL;
+  }
 
   select_record *select_read (select_stuff *);
   select_record *select_write (select_stuff *);

winsup/cygwin/fhandler_console.cc

@@ -196,6 +196,7 @@ fhandler_console::setup ()
 	  con.meta_mask |= RIGHT_ALT_PRESSED;
 	con.set_default_attr ();
 	con.backspace_keycode = CERASE;
+	con.cons_rapoi = NULL;
 	shared_console_info->tty_min_state.is_console = true;
       }
 }
@@ -310,6 +311,14 @@ fhandler_console::read (void *pv, size_t& buflen)
   int ch;
   set_input_state ();
 
+  /* Check console read-ahead buffer filled from terminal requests */
+  if (con.cons_rapoi && *con.cons_rapoi)
+    {
+      *buf = *con.cons_rapoi++;
+      buflen = 1;
+      return;
+    }
+
   int copied_chars = get_readahead_into_buffer (buf, buflen);
 
   if (copied_chars)
@@ -1899,8 +1908,11 @@ fhandler_console::char_command (char c)
 	strcpy (buf, "\033[?6c");
       /* The generated report needs to be injected for read-ahead into the
 	 fhandler_console object associated with standard input.
-	 The current call does not work. */
+	 So puts_readahead does not work.
-      puts_readahead (buf);
+	 Use a common console read-ahead buffer instead. */
+      con.cons_rapoi = NULL;
+      strcpy (con.cons_rabuf, buf);
+      con.cons_rapoi = con.cons_rabuf;
       break;
     case 'n':
       switch (con.args[0])
@@ -1910,9 +1922,11 @@ fhandler_console::char_command (char c)
 	  y -= con.b.srWindow.Top;
 	  /* x -= con.b.srWindow.Left;		// not available yet */
 	  __small_sprintf (buf, "\033[%d;%dR", y + 1, x + 1);
-	  puts_readahead (buf);
+	  con.cons_rapoi = NULL;
+	  strcpy (con.cons_rabuf, buf);
+	  con.cons_rapoi = con.cons_rabuf;
 	  break;
-      default:
+	default:
 	  goto bad_escape;
 	}
       break;

winsup/cygwin/select.cc

@@ -845,6 +845,12 @@ peek_console (select_record *me, bool)
   if (!me->read_selected)
     return me->write_ready;
 
+  if (fh->get_cons_readahead_valid ())
+    {
+      select_printf ("cons_readahead");
+      return me->read_ready = true;
+    }
+
   if (fh->get_readahead_valid ())
     {
       select_printf ("readahead");