enable unsafe_op_in_unsafe_fn lint

src/libstd/fs.rs

@@ -8,6 +8,7 @@
 //! extension traits of `std::os::$platform`.
 
 #![stable(feature = "rust1", since = "1.0.0")]
+#![deny(unsafe_op_in_unsafe_fn)]
 
 use crate::ffi::OsString;
 use crate::fmt;

src/libstd/lib.rs

@@ -319,6 +319,7 @@
 #![feature(track_caller)]
 #![feature(try_reserve)]
 #![feature(unboxed_closures)]
+#![feature(unsafe_block_in_unsafe_fn)]
 #![feature(untagged_unions)]
 #![feature(unwind_attributes)]
 #![feature(vec_into_raw_parts)]