Rollup merge of rust-lang#112621 - GrigorenkoPV:env, r=jyn514

Mention `env!` in `option_env!`'s docs

`env!` mentions that there is an alternative that returns an `Option<...>` instead of emitting a compile error.

Now `option_env!` also mentions that there is an alternative that emits a compile error instead of returning an `Option<...>`.

Author: matthiaskrgr

library/core/src/macros/mod.rs

@@ -960,6 +960,8 @@ pub(crate) mod builtin {
     ///
     /// A compile time error is never emitted when using this macro regardless
     /// of whether the environment variable is present or not.
+    /// To emit a compile error if the environment variable is not present,
+    /// use the [`env!`] macro instead.
     ///
     /// # Examples
     ///