One attr test (version 2.5.1) fails with musl (I tested with version 1.2.3):

```
FAIL: test/attr
===============

[9] $ mkdir d -- ok
[10] $ cd d -- ok
[12] $ touch f -- ok
[13] $ setfattr -n user -v value f -- failed
setfattr: f: Not supported                                                         != setfattr: f: Operation not supported
[16] $ setfattr -n user. -v value f -- ok
[19] $ setfattr -n user.name f -- ok
<snip>
```

It fails because musl stringifies ENOTSUPP as "Not supported"[1]
and not as "Operation not supported" which the test expects. I'm not very knowledgable in this area, but I think POSIX doesn't mandate the exact string representation of the error numbers? Would it be possible to make the test allow both versions?

Best regards,
Marvin

[1] https://git.musl-libc.org/cgit/musl/tree/src/errno/__strerror.h#n85