[clang] [llvm] [AArch64] Add ability to list extensions enabled for a target (PR #95805)

[Jonathan Thackray via cfe-commits]

jthackray wrote:

This is a good idea. Happy to approve, once all the FIXMEs are removed, since others have already made many salient suggestions, which I agree with.

https://github.com/llvm/llvm-project/pull/95805