hash: Upgrade xxHash to 0.8.2

[TimWolla]

No description provided.

[TimWolla]

0.8.3 changes the internal struct, which breaks serialization, because serialization touches the internal fields of the opaque struct …

[ndossche]

I'll have a proper look later, but the xxhash files had some manual patches done to them by various people (mostly backport probably); see #18842

[TimWolla]

but the xxhash files had some manual patches done to them

If it's not asserted by CI it doesn't exist 😉

[ndossche]

Then half of php does not exist

[ndossche]

I went through the patches that went in after xxhash 0.8.1 went in:

• a839230 which was pulled from upstream, so OK included
• 7638640 also from upstream, so OK included
• adcb38b also upstream
• a82d864 which also has a corresponding upstream PR
• afb1c57 which is mine, part of this modifies xxhash.h to work around a (older) compiler bug. I think it's fine to drop this patch.

I then compared with 0.8.2 upstream and found the sources match.

0.8.3 changes the internal struct, which breaks serialization, because serialization touches the internal fields of the opaque struct …

I see. That's unfortunate. I haven't looked at this yet but I wonder if there's a migration path possible. 0.8.3 contains a bugfix for XXH3_128bits_withSecretandSeed but it doesn't seem like we use that directly.