[C++] Bump vendored version of xxhash to latest

[raulcd]

Describe the enhancement requested

We are using an older version. The vendored xxhash latest version is:

• https://github.com/Cyan4973/xxHash/releases/tag/v0.8.3

The upgrade might also come with some improvements / fixes.

First discussed here:

• [CI][C++] test-conda-cpp-valgrind fails building vendored/xxhash.h #47475 (comment)

Component(s)

C++

[pitrou]

Issue resolved by pull request 47476
#47476