cp: close file descriptors after cow on linux

Instead of using into_raw_fd(), which transfers ownership and
requires us to close the file descriptor manually,
use as_raw_fd(), which does not transfer ownership to us but drops the
file descriptor when the original file is dropped (in our case at the
end of the function).

src/uu/cp/src/cp.rs

@@ -41,7 +41,7 @@ use std::io;
 use std::io::{stdin, stdout, Write};
 use std::mem;
 #[cfg(target_os = "linux")]
-use std::os::unix::io::IntoRawFd;
+use std::os::unix::io::AsRawFd;
 #[cfg(windows)]
 use std::os::windows::ffi::OsStrExt;
 use std::path::{Path, PathBuf, StripPrefixError};
@@ -1261,14 +1261,14 @@ fn copy_helper(source: &Path, dest: &Path, options: &Options) -> CopyResult<()>
 fn copy_on_write_linux(source: &Path, dest: &Path, mode: ReflinkMode) -> CopyResult<()> {
     debug_assert!(mode != ReflinkMode::Never);
 
-    let src_file = File::open(source).unwrap().into_raw_fd();
+    let src_file = File::open(source).unwrap().as_raw_fd();
     let dst_file = OpenOptions::new()
         .write(true)
         .truncate(false)
         .create(true)
         .open(dest)
         .unwrap()
-        .into_raw_fd();
+        .as_raw_fd();
     match mode {
         ReflinkMode::Always => unsafe {
             let result = ficlone(dst_file, src_file as *const i32);