[llvm] langref updates for aarch64 trampoline (PR #139740)

[Eli Friedman via llvm-commits]

================
@@ -410,8 +410,8 @@ added in the future:
       calling convention: on most platforms, they are not preserved and need to
       be saved by the caller, but on Windows, xmm6-xmm15 are preserved.
 
-    - On AArch64 the callee preserve all general purpose registers, except X0-X8
-      and X16-X18.
+    - On AArch64 the callee preserve all general purpose registers, except
+      X0-X8 and X16-X18. Not allowed with nest.
----------------
efriedma-quic wrote:

```suggestion
      X0-X8 and X16-X18. Not allowed with ``nest``.
```

https://github.com/llvm/llvm-project/pull/139740