Add compat notes for lld and MSG_NOSIGNAL

Author: Mark-Simulacrum

RELEASES.md

@@ -112,7 +112,12 @@ Rustdoc
 
 Compatibility Notes
 -------------------
+- [Use `lld` by default on `x86_64-unknown-linux-gnu`](https://github.com/rust-lang/rust/pull/140525).
+  See also <https://blog.rust-lang.org/2025/09/01/rust-lld-on-1.90.0-stable/>.
 - [Make `core::iter::Fuse`'s `Default` impl construct `I::default()` internally as promised in the docs instead of always being empty](https://github.com/rust-lang/rust/pull/140985)
+- [Set `MSG_NOSIGNAL` for `UnixStream`](https://github.com/rust-lang/rust/pull/140005)
+  This may change program behavior but results in the same behavior as other primitives (e.g., stdout, network sockets).
+  Programs relying on signals to terminate them should update handling of sockets to handle errors on write by exiting.
 - [On Unix `std::env::home_dir` will use the fallback if the `HOME` environment variable is empty](https://github.com/rust-lang/rust/pull/141840)
 - We now [reject unsupported `extern "{abi}"`s consistently in all positions](https://github.com/rust-lang/rust/pull/142134). This primarily affects the use of implementing traits on an `extern "{abi}"` function pointer, like `extern "stdcall" fn()`, on a platform that doesn't support that, like aarch64-unknown-linux-gnu. Direct usage of these unsupported ABI strings by declaring or defining functions was already rejected, so this is only a change for consistency.
 - [const-eval: error when initializing a static writes to that static](https://github.com/rust-lang/rust/pull/143084)