[clang] [compiler-rt] [llvm] [FMV][AArch64] Unify features memtag and memtag2. (PR #112511)

[Alexandros Lamprineas via cfe-commits]

labrinea wrote:

> I don't understand this distinction: why is FMV seen as user-space only?

I had to clarify this with @Wilco1 and @DanielKristofKiss. My understanding is that FMV implementations which rely on ifuncs (Linux) only work in address spaces where a dynamic linker can be used. This limitation rules out OS and baremetal environments. However, there are FMV implementations which emulate ifuncs via function pointers (Windows), but the specification must be possible to implement on all platforms, and therefore it is bound by the ifunc limitation.

https://github.com/llvm/llvm-project/pull/112511