in pathconf, -1, not 0, means unsupported.. syncio presumably works, too.
[musl] / src / errno /
drwxr-xr-x   ..
-rw-r--r-- 145 __errno_location.c
-rw-r--r-- 3824 __strerror.h
-rw-r--r-- 371 strerror.c