[Diffusion] rL196996: Move mips' datalayout computation out of line and add comments.

[Daniel Sanders]

> No, sorry about that. The intension was for this to produce an identical string.
> 
> I was curious how could this not have causes a test failure, then I
> noticed that DataLayout::init looks like:
> 
> ...
>  // Default alignments
> ...
> setAlignment(FLOAT_ALIGN,    16, 16, 128);
> ...
> parseSpecifier(Desc);
> 
> So f:128:128:128 is one of the defaults.

That's ok. I would have expected some failures too but if it's only repeating the defaults then there's no problem.

Thanks for tidying up this code.

> I think it is actually a bit better to use the simpler string.
> Otherwise we get the impression that ABI_N64 is different when it is
> actually just being explicit while the other abi is implicit, but this
> is your call. Do you want me to add this back?

I agree, there's no need to redundantly specify the default values. I also see no reason to put it back only to re-remove it again.