fix: avoid *at functions for better compatibility

As far as I can tell, `*at` syscalls are equivalent to their
counterparts when they're called relative to the current working
directory, so this shouldn't matter. We only _need_ the `*at` syscall
for `renameat2` to pass some flags.

fixes #246

src/file/imp/unix.rs

@@ -14,7 +14,7 @@ use crate::util;
 use std::path::Path;
 
 #[cfg(not(target_os = "redox"))]
-use rustix::fs::{linkat, renameat, unlinkat, AtFlags, CWD};
+use rustix::fs::{link, rename, unlink};
 
 pub fn create_named(path: &Path, open_options: &mut OpenOptions) -> io::Result<File> {
     open_options.read(true).write(true).create_new(true);
@@ -103,12 +103,13 @@ pub fn reopen(_file: &File, _path: &Path) -> io::Result<File> {
 #[cfg(not(target_os = "redox"))]
 pub fn persist(old_path: &Path, new_path: &Path, overwrite: bool) -> io::Result<()> {
     if overwrite {
-        renameat(CWD, old_path, CWD, new_path)?;
+        rename(old_path, new_path)?;
     } else {
         // On Linux, use `renameat_with` to avoid overwriting an existing name,
         // if the kernel and the filesystem support it.
         #[cfg(any(target_os = "android", target_os = "linux"))]
         {
+            use rustix::fs::CWD;
             use rustix::fs::{renameat_with, RenameFlags};
             use rustix::io::Errno;
             use std::sync::atomic::{AtomicBool, Ordering::Relaxed};
@@ -124,12 +125,12 @@ pub fn persist(old_path: &Path, new_path: &Path, overwrite: bool) -> io::Result<
             }
         }
 
-        // Otherwise use `linkat` to create the new filesystem name, which
-        // will fail if the name already exists, and then `unlinkat` to remove
+        // Otherwise use `link` to create the new filesystem name, which
+        // will fail if the name already exists, and then `unlink` to remove
         // the old name.
-        linkat(CWD, old_path, CWD, new_path, AtFlags::empty())?;
+        link(old_path, new_path)?;
         // Ignore unlink errors. Can we do better?
-        let _ = unlinkat(CWD, old_path, AtFlags::empty());
+        let _ = unlink(old_path);
     }
     Ok(())
 }