[clang] [Clang][Driver][AArch64] Add support for aarch64-amazon-linux triple (PR #109263)

[Benjamin Herrenschmidt via cfe-commits]

ozbenh wrote:

@MaskRay Fedora and RHEL also don't use -gnu ... we had no idea this mattered when we did this and we can't really change it at this point without breaking customers.

I would understand applying the rule for new use cases, but this is an established one that cannot be fixed, and an existing discrepancy in clang since it *does* already have the amazon linux triplet for x86_64, just missing the aarch64 one.

https://github.com/llvm/llvm-project/pull/109263