Update library/std/src/sys/pal/common/exit_guard.rs

Co-authored-by: Ralf Jung <post@ralfj.de>

std/src/sys/pal/common/exit_guard.rs

@@ -2,12 +2,14 @@ cfg_if::cfg_if! {
     if #[cfg(target_os = "linux")] {
         /// Mitigation for <https://github.com/rust-lang/rust/issues/126600>
         ///
-        /// On UNIX-like platforms (where `libc::exit` may not be thread-safe), ensure that only one
+        /// On glibc, `libc::exit` has been observed to not always be thread-safe.
+        /// It is currently unclear whether that is a glibc bug or allowed by the standard.
+        /// To mitigate this problem, we ensure that only one
         /// Rust thread calls `libc::exit` (or returns from `main`) by calling this function before
         /// calling `libc::exit` (or returning from `main`).
         ///
-        /// Technically not enough to ensure soundness, since other code directly calling
-        /// libc::exit will still race with this.
+        /// Technically, this is not enough to ensure soundness, since other code directly calling
+        /// `libc::exit` will still race with this.
         ///
         /// *This function does not itself call `libc::exit`.* This is so it can also be used
         /// to guard returning from `main`.