[XS] Change in coreboot[main]: stddef.h: Introduce nullptr constant

[Nico Huber (Code Review)]

Attention is currently required from: Elyes Haouas, Felix Singer, Jakub Czapiga, Julius Werner, Martin L Roth, Maximilian Brune.

Nico Huber has posted comments on this change by Elyes Haouas. ( https://review.coreboot.org/c/coreboot/+/83459?usp=email )

Change subject: stddef.h: Introduce nullptr constant
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Patch Set 26:

(1 comment)

File src/include/stddef.h:

https://review.coreboot.org/c/coreboot/+/83459/comment/d4972a81_706e3a95?usp... :
PS26, Line 25: #define nullptr ((void *)0)
> I don't remember exactly what was said but I agree with Felix here: I think the important part is th […]

To be clear, my concern is only about the `#define nullptr` on the old path, not the C23 path.

As Julius suggests this may help with imported code, but that means we'd have to
weigh if it's more likely to be code that expects `nullptr` to be provided by
`stddef.h` (why would it be? it's not in any standard AFAIK) or code that may
even have a completely different use for this identifier. Seems rather undecidable
to me, so I'd suggest to do less and deal with imported code when it comes.