Cranelift: emit_small_memory_copy ignores alignment

`cranelift_frontend::FunctionBuilder::emit_small_memory_copy`([documentation](https://docs.rs/cranelift-frontend/0.78.0/cranelift_frontend/struct.FunctionBuilder.html#method.emit_small_memory_copy)) takes the arguments `dest_align` and `src_align`, which it uses only for an assertion and then ignores. It chooses an access size which may be larger than the alignment and calls `flags.set_aligned();` and proceeds to doing unaligned memory access. This seems to be a mistake.

Reported by Veverak at https://bytecodealliance.zulipchat.com/#narrow/stream/217117-cranelift/topic/emit_small_memory_copy.20ignores.20alignment/near/263576215