[llvm] [AArch64][MachinePipeliner] Add pipeliner support for AArch64 (PR #79589)

[via llvm-commits]

bcahoon wrote:

> I have a question about the build options of llvm-test-suites, why set pipeliner-enable-copytophi flag to 0. In some cases, this can lead to a compilation failure because the compiler may use registers before register definitions.

The intent of that flag is that it should not affect correctness. Perhaps setting it to 0 exposes a different bug?

https://github.com/llvm/llvm-project/pull/79589