Rustify some functions (following TODO)

src/header/stdlib/mod.rs

@@ -791,20 +791,12 @@ pub unsafe extern "C" fn mkostemps(
     suffix_len: c_int,
     mut flags: c_int,
 ) -> c_int {
-    // TODO: Rustify impl
-
     flags &= !O_ACCMODE;
     flags |= O_RDWR | O_CREAT | O_EXCL;
 
     inner_mktemp(name, suffix_len, || {
         let name = CStr::from_ptr(name);
-        let fd = Sys::open(name, flags, 0o600).or_minus_one_errno();
-
-        if fd >= 0 {
-            Some(fd)
-        } else {
-            None
-        }
+        Sys::open(name, flags, 0o600).ok()
     })
     .unwrap_or(-1)
 }