[llvm] [llvm] Remove `inline constexpr` from AArch64TargetParser.h (PR #71602)

[Tomas Matheson via llvm-commits]

tmatheson-arm wrote:

Just to add some context: IIRC, `inline constexpr` was used to guarantee that these objects had unique addresses, which was necessary because some equality checks were based on address. That turned out to be unworkable and was removed, so I think the `inline constexpr` is no longer necessary. It wasn't for optimisation.

https://github.com/llvm/llvm-project/pull/71602