in pathconf, -1, not 0, means unsupported.. syncio presumably works, too.
[musl] / src / ldso /
drwxr-xr-x   ..
-rw-r--r-- 132 dlsym.c
-rw-r--r-- 17491 dynlink.c
drwxr-xr-x - i386
-rw-r--r-- 105 start.c
drwxr-xr-x - x86_64