Rollup merge of rust-lang#74979 - maekawatoshiki:fix, r=Mark-Simulacrum

`#![deny(unsafe_op_in_unsafe_fn)]` in sys/hermit

Partial fix of rust-lang#73904.

This encloses ``unsafe`` operations in ``unsafe fn`` in ``sys/hermit``.
Some unsafe blocks are not well documented because some system-based functions lack documents.

Author: JohnTitor

library/std/src/sys/hermit/mod.rs

@@ -13,6 +13,8 @@
 //! compiling for wasm. That way it's a compile time error for something that's
 //! guaranteed to be a runtime error!
 
+#![allow(unsafe_op_in_unsafe_fn)]
+
 use crate::intrinsics;
 use crate::os::raw::c_char;