Pseudo-Terminals are broken, please backport fix from upstream

[Daniel Gibson]

Pseudo Terminals misbehave with lines that have exactly 65 characters *including* the terminating newline.
This bug has existed since Kernel 5.12, see https://bugzilla.kernel.org/show_bug.cgi?id=215611 for details.

It has recently been fixed, see https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3593030761630e09200072a4bd06468892c27be3

This fix has also been backported into official branches of older (LTS) kernel versions (5.10, 5.15, 5.16), see e.g. https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v5.16.14&id=ee421a75a740d6d8579fb1426141312313287de2

Please backport it to the Ubuntu branch of 5.13 so the fix gets into 20.04LTS and I can finally use gdb in Eclipse CDT again ;)

Cheers,
Daniel

[Daniel Gibson (metalcaedes)]

Added testcase and patch