Enable Kernels to be built on top of kernlSpec arguments

[anutosh491]

Screen.Recording.2025-04-17.at.1.47.31.PM.mp4

Demo above : Shows 3 xeus-cpp-lite kernels built (all use different flags -std=c++17/20/23)

On top of which xcpp20 is built using the -msimd128 flag (required for running xsimd in the browser)

  "argv": [
      "@XEUS_CPP_KERNELSPEC_PATH@xcpp",
      "-resource-dir", "@XEUS_CPP_RESOURCE_DIR@",
      "-std=c++20", "-msimd128"
  ],
  
// instead of 

  "argv": [
      "@XEUS_CPP_KERNELSPEC_PATH@xcpp",
      "-resource-dir", "@XEUS_CPP_RESOURCE_DIR@",
      "-std=c++23", 
  ],

So xcpp20 kernel would work but xcpp23 wouldn't !

[anutosh491]

Refer #jupyter-xeus/xeus-lite#16 and #compiler-research/xeus-cpp#290

[martinRenou]

Small suggestion to hopefully make the CI pass, and support old kernels

[martinRenou]

Thanks!

[martinRenou]

@meeseeksdev please backport to 3.x

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 3.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 ddcb13c5cfe8bc3fc6c666ed7360ca222b945fbd

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #210: Enable Kernels to be built on top of kernlSpec arguments'

4. Push to a named branch:

git push YOURFORK 3.x:auto-backport-of-pr-210-on-3.x

5. Create a PR against branch 3.x, I would have named this PR:

"Backport PR #210 on branch 3.x (Enable Kernels to be built on top of kernlSpec arguments)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.