[AArch64] Add some release notes items (#79983)

Author: momchil-velikov

clang/docs/ReleaseNotes.rst

@@ -1167,6 +1167,11 @@ Arm and AArch64 Support
   * Cortex-A720 (cortex-a720).
   * Cortex-X4 (cortex-x4).
 
+- Alpha support has been added for SVE2.1 intrinsics.
+
+- Support has been added for `-fstack-clash-protection` and `-mstack-probe-size`
+  command line options.
+
 - Function Multi Versioning has been extended to support Load-Acquire RCpc
   instructions v3 (rcpc3) as well as Memory Copy and Memory Set Acceleration
   instructions (mops) when targeting AArch64. The feature identifiers (in

llvm/docs/ReleaseNotes.rst

@@ -105,6 +105,14 @@ Changes to the AArch64 Backend
   Armv9.0a has the same features enabled as Armv8.5a, with the exception
   of crypto.
 
+* Assembler/disassembler support has been added for 2023 architecture
+  extensions.
+
+* Support has been added for Stack Clash Protection. During function frame
+  creation and dynamic stack allocations, the compiler will issue memory
+  accesses at reguilar intervals so that a guard area at the top of the stack
+  can't be skipped over.
+
 Changes to the AMDGPU Backend
 -----------------------------