[llvm] [llubi] Add support for byte types (PR #200672)

[Ralf Jung via llvm-commits]

RalfJung wrote:

> On the contrary, it is for byte-type load/store. We don't have code directly converting between byte SSA values and integer values. They are always serialized into memory representation (toBytes), then loaded from the memory (fromBytes).

Hm, then I don't understand why endianess would ever matter. `b64` is just going to be 8 bytes in the same order that they have in memory. Endianess is relevant for integers (and floats?) but not for anything else.

https://github.com/llvm/llvm-project/pull/200672