[llvm] [AArch64] Define high bits of FPR and GPR registers (take 2) (PR #114827)

[Vitaly Buka via llvm-commits]

vitalybuka wrote:

This patch makes libcxx tests to timeouts here
https://lab.llvm.org/buildbot/#/builders/85

Many tests slowed down 10x or more.

https://github.com/llvm/llvm-project/pull/114827