ttyname_r returning EINVAL

[Simon Josefsson]

As explained as 4) in this e-mail:

https://lists.gnu.org/archive/html/bug-gnulib/2011-08/msg00027.html

it seems like the ttyname_r function returns EINVAL when the provided
buffer is too small.

This doesn't seem consistent with the specifcation at:

http://pubs.opengroup.org/onlinepubs/9699919799/functions/ttyname.html

Instead, it seems this should be ERANGE?

[ERANGE]
    The value of namesize is smaller than the length of the string to be
    returned including the terminating null character.

/Simon