[2.26 COMMITTED] manual: Update to mention ENODEV for ttyname and ttyname_r

[Florian Weimer]

From: Luke Shumaker <lukeshu@parabola.nu>

Commit 15e9a4f378c8607c2ae1aa465436af4321db0e23 introduced ENODEV as a possible
error condition for ttyname and ttyname_r. Update the manual to mention this GNU
extension.

Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
(cherry picked from commit 495a56fdeb05d20a88304ff5da577d23a8e81ae1)

2017-11-15  Luke Shumaker  <lukeshu@parabola.nu>

	* manual/terminal.texi (Is It a Terminal):
	Mention ENODEV for ttyname and ttyname_r.

diff --git a/manual/terminal.texi b/manual/terminal.texi
index 4fef5045b8..4aace48b14 100644
--- a/manual/terminal.texi
+++ b/manual/terminal.texi
@@ -109,6 +109,11 @@ The @var{filedes} is not associated with a terminal.
 @item ERANGE
 The buffer length @var{len} is too small to store the string to be
 returned.
+
+@item ENODEV
+The @var{filedes} is associated with a terminal device that is a slave
+pseudo-terminal, but the file name associated with that device could
+not be determined.  This is a GNU extension.
 @end table
 @end deftypefun