DragonFlyBSD

tcsetattr() and tcgetattr() are documented to fail as follows:

Upon successful completion, the functions tcgetattr() and tcsetattr()
     return a value of 0.  Otherwise, they return -1 and the global variable
     errno is set to indicate the error, as follows:

...

[ENOTTY]           The file associated with the fd argument to
                        tcgetattr() or tcsetattr() is not a terminal.

which matches POSIX, but they do not set errno correctly:

$ cc -otcerror tcerror.c
$ ./tcerror
OK: tcgetattr on /dev/null failed as expected
FAIL: tcgetattr on /dev/null set errno incorrectly: Operation not supported by device
OK: tcsetattr failed as expected
FAIL: tcsetattr failure set errno incorrectly: Operation not supported by device
$ uname -a
DragonFly 5.8-RELEASE DragonFly v5.8.3-RELEASE #10: Thu Sep 24 19:19:45 EDT 2020 root@www.shiningsilence.com:/usr/obj/home/justin/release/5_8/sys/X86_64_GENERIC x86_64

This was discovered while diagnosing perl test failures.