refactor: remove macOS ≤ 13 fallback for mknodat/mkfifoat

macOS 13 and earlier are EOL. Use c::mknodat directly via libc
without weak-linking, matching other platforms.

Author: mattsu2020

src/backend/libc/fs/syscalls.rs

@@ -1209,37 +1209,6 @@ pub(crate) fn mknodat(
     mode: Mode,
     dev: Dev,
 ) -> io::Result<()> {
-    // macOS ≤ 13 lacks `mknodat`.
-    #[cfg(target_os = "macos")]
-    unsafe {
-        weak! {
-            fn mknodat(
-                c::c_int,
-                *const ffi::c_char,
-                c::mode_t,
-                c::dev_t
-            ) -> c::c_int
-        }
-        if let Some(libc_mknodat) = mknodat.get() {
-            return ret(libc_mknodat(
-                borrowed_fd(dirfd),
-                c_str(path),
-                (mode.bits() | file_type.as_raw_mode()) as c::mode_t,
-                dev.try_into().map_err(|_e| io::Errno::PERM)?,
-            ));
-        }
-        // Otherwise, see if we can emulate the `AT_FDCWD` case.
-        if borrowed_fd(dirfd) != c::AT_FDCWD {
-            return Err(io::Errno::NOSYS);
-        }
-        ret(c::mknod(
-            c_str(path),
-            (mode.bits() | file_type.as_raw_mode()) as c::mode_t,
-            dev.try_into().map_err(|_e| io::Errno::PERM)?,
-        ))
-    }
-
-    #[cfg(not(target_os = "macos"))]
     unsafe {
         ret(c::mknodat(
             borrowed_fd(dirfd),