Rollup merge of rust-lang#119590 - ChrisDenton:cfg-target-abi, r=Nilstrieb

Stabilize `cfg_target_abi`

This stabilizes the `cfg` option called `target_abi`:

```rust
#[cfg(target_abi = "eabihf")]
```

Tracking issue: rust-lang#80970

fixes rust-lang#78791
resolves rust-lang#80970

Author: matthiaskrgr

unwind/src/lib.rs

@@ -3,7 +3,7 @@
 #![feature(link_cfg)]
 #![feature(staged_api)]
 #![feature(c_unwind)]
-#![feature(cfg_target_abi)]
+#![cfg_attr(bootstrap, feature(cfg_target_abi))]
 #![feature(strict_provenance)]
 #![cfg_attr(not(target_env = "msvc"), feature(libc))]
 #![allow(internal_features)]