[Clang][Docs] Add release note for execute-only support on AArch64 (#134802)

Author: Il-Capitano

clang/docs/ReleaseNotes.rst

@@ -219,6 +219,8 @@ Modified Compiler Flags
 
 - `-Wpadded` option implemented for the `x86_64-windows-msvc` target. Fixes #61702
 
+- The ``-mexecute-only`` and ``-mpure-code`` flags are now accepted for AArch64 targets. (#GH125688)
+
 Removed Compiler Flags
 -------------------------
 
@@ -569,6 +571,9 @@ Arm and AArch64 Support
 
 -  Support for __ptrauth type qualifier has been added.
 
+- For AArch64, added support for generating executable-only code sections by using the
+  ``-mexecute-only`` or ``-mpure-code`` compiler flags. (#GH125688)
+
 Android Support
 ^^^^^^^^^^^^^^^