Opt memcpy memmove

[ZERICO2005]

makes memcpy 1F faster and memmove 2F faster in the common case.

The timings can be adjusted slightly for memmove (src != dst version), depending on which is faster/better on average

    ; src >= dst | LDIR | 30F + 15R + 1 ; jr false
    ; src <  dst | LDDR | 34F + 12R + 2 ; jr true

    ; src >= dst | LDIR | 31F + 15R + 2 ; jr true
    ; src <  dst | LDDR | 33F + 12R + 1 ; jr false

[mateoconlechuga]

Looks good, let's remove the PREFER_OS_LIBC option and just use these directly. I assume these optimizations are valid @calc84maniac?

[calc84maniac]

This comment is no longer applicable, right?

[ZERICO2005]

Yeah, I will fix that

[calc84maniac]

If the two memmove implementations are now identical aside from a ret z, maybe put only that in the .if 0 to keep it more maintainable (or remove the one we're not using entirely)

[ZERICO2005]

They differ slightly. The src == dst version has to have to jr to LDDR and fall-through to LDIR to keep timings equal. Whereas the src != dst version can either have the LDIR or LDDR path be the faster path (by 1F + 1)

The LDIR path has an extra 3R and the LDDR path has an extra 3F, so I wasn't sure which would be better to allocate the 1F + 1 savings to