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

[Csanád Hajdú via cfe-commits]

Il-Capitano wrote:

> There is a `Arm and AArch64 Support` section too, is it worth adding a note there either instead or as well? It could maybe just be a note that points back to the Modified Compiler Flags section.

Thanks, I didn't notice that section.

I simplified the note in "Modified Compiler Flags" and added one in "Arm and AArch64 Support".

https://github.com/llvm/llvm-project/pull/134802