[lld] [lld][Hexagon] Add "hexagonlinux" emulation alias (PR #185743)

[Fangrui Song via llvm-commits]

MaskRay wrote:

We actively discourage unnecessary emulations and linker-based discrepancies. Instead, we advocate for passing explicit linker options directly through the Clang driver. In addition, I don't see "hexagonlinux" in llvm-project yet.

https://github.com/llvm/llvm-project/pull/185743