abort docs: Do not claim that intrinsics::abort is always a debug trap

As per discussion here
 https://github.com/rust-lang/rust/pull/85377#pullrequestreview-660460501

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

library/core/src/intrinsics.rs

@@ -720,7 +720,9 @@ extern "rust-intrinsic" {
     /// [`std::process::abort`](../../std/process/fn.abort.html) is to be preferred if possible,
     /// as its behaviour is more user-friendly and more stable.
     ///
-    /// The current implementation of `intrinsics::abort` (ab)uses a debug trap.  On Unix, the
+    /// The current implementation of `intrinsics::abort` (ab)uses a debug trap
+    /// on some popular platforms.
+    /// On Unix, the
     /// process will probably die of a signal like `SIGABRT`, `SIGILL`, `SIGTRAP`, `SIGSEGV` or
     /// `SIGBUS`.  The precise behaviour is not guaranteed and not stable.
     pub fn abort() -> !;