[llvm] [LLVM] Add zstd compressed frame magic to LLVM magic (PR #222773)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

I was thinking about adding `zlib`, but I couldn't find a single dedicated magic bytestream that matched it like `zstd` had. I think it *does* have some bytes to indicate headers, but they aren't as uniquely identifiable. The usage in the offloading case was intended to be like 'Is it compressed? It's either zlib or zstd' and I figured anything that wasn't valid would probably error faithfully there.

I can try to see if adding zlib-flavored magic works, but I think it's only two bytes of header.

https://github.com/llvm/llvm-project/pull/222773