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

[Fangrui Song via cfe-commits]

MaskRay wrote:

> The behviour was diverged between X86 and aarch64: prior to this patch, a standard clang with no configuration works on x86 but not aarch64 amazon linux; the latter fails to find C++ headers and libraries.

This is not an issue of the source code. The system needs to do `-DLLVM_DEFAULT_TARGET_TRIPLE=aarch64-amazon-linux`. The comment is here for reasons as it doesn't scale to encode every possible target triple.

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