[clang] Add armagicpu to release notes (PR #205599)

[Volodymyr Turanskyy via cfe-commits]

================
@@ -888,6 +888,8 @@ X86 Support
 Arm and AArch64 Support
 ^^^^^^^^^^^^^^^^^^^^^^^
 
+- Added support for ``-mcpu=armagicpu`` as an alias for ``neoverse-v3ae``.
----------------
voltur01 wrote:

```suggestion
Added support for the Arm AGI CPU via the ``-mcpu=armagicpu`` command-line option.
```

https://github.com/llvm/llvm-project/pull/205599