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

[Joseph Huber via llvm-commits]

jhuber6 wrote:

I tried to use the headers that LLVM emits as something to key off of, it's not as uniquely identifiable as `zstd`, but if you're looking for specific magic in a bytestream it will still tell you that it's `zlib`. PTAL.

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