Implement more of the hint/no-op intrinsics

[jberthold]

A number of rustc intrinsics represent mere hints to the compiler and are actual no-ops for the semantics.

• cold_path (observed, required for P-token)
• likely, unlikely (returning bool argument)
• prefetch_* (no-op)

Only cold_path is required at this point.
At the same time, the intrinsics implementations should be moved to their own module intrinsics.md (requiring an import of the data.md module for projection traversals, and its dependent value.md for values).

[Stevengre]

• intrinsic bswap is needed to run the following program:

fn main() {
    let value = 0x0123_4567_89AB_CDEF_u64;

    let native_bytes = value.to_ne_bytes();
    assert_eq!(u64::from_ne_bytes(native_bytes), value);

    let little_bytes = value.to_le_bytes();
    assert_eq!(u64::from_le_bytes(little_bytes), value);

    let big_bytes = value.to_be_bytes();
    assert_eq!(u64::from_be_bytes(big_bytes), value);
}

[dkcumming]

@Stevengre that comment seems to refer to a intrinsic that would need a body implemented no? It wouldn't be a NO OP right?

[Stevengre]

But we can also implement it in k without body, I think.

[dkcumming]

@Stevengre But it is not a NOOP? It reverses the byte order right?

[Stevengre]

Yes, I think so.