Added fixes for building with clang 19

[vakokako]

Fixes build issues with clang 19, discussed in #2783, #2804.

[vincent-mayer]

Hey @JohanMabille, @SylvainCorlay can this move forward, or is anything blocking it? It would enable us to move to clang19 :)

[emmenlau]

Just to note, the patch here is rather minimal, it just enables some ifdef-case that previously did not include clang 19.

Maybe that helps the review?

[jtramm]

This would be great to get merged in, as OpenMC continues to have issues (exasmr/openmc#52) and (openmc-dev/openmc#3183) with LLVM 19 due to this. We can pass -fno-relaxed-template-template-args as a workaround, but this argument is deprecated and now removed in LLVM 21, so we would like to remove this arg from our build to stay up to date.

[YesserLab]

Can we please merge that ? This is starting to block us as well.

[YesserLab]

bump 🙂

[JohanMabille]

Hi everyone,

Sorry for this very late reply and the inconvenience, I've been swamped with other tasks, but now I'm back on xtensor. I could not solve the conflicts on this PR (because I cannot push on the branch), so I opened a new PR that superseds this one (@vakokako like for your previous PR, I cherry-picked your commit so that you keep the credit for the fix).

#2833 has been merged on top of backard incompatible changes that reorganizes the code (basically moving headers to dedicated folders, building with C++17 by default, and replacing backported features with their standard implementation). If you need this change in a backward copatible branch, let me know, I can backport it and quickly release a 0.25.1.

[emmenlau]

@JohanMabille awesome, thanks!

[JohanMabille]

xtensor 0.26 has been released, it includes this fix. Notice that we have upgraded to C++17, and we plan to move to C++20 quickly.