Make XEUS_CPP_RESOURCE_DIR a user configurable option

[mcbarton]

Description

Please include a summary of changes, motivation and context for this PR.

The llvm resource directory is now unconditionally assumed to be installed in the CMAKE_INSTALL_PREFIX . This has caused problems in CppInterOp where we do not install it in this location. Therefore this PR makes the clang resource directory an option that can be provided by the user, and fallsback to assuming its in the install prefix if not defined.

Fixes # (issue)

Type of change

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• Bug fix
• New feature
• Added/removed dependencies
• Required documentation updates

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.78%. Comparing base (51aeae3) to head (765e90d).

Additional details and impacted files

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  Coverage   81.78%   81.78%           
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  Files          20       20           
  Lines         950      950           
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  Misses        173      173           

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[mcbarton]

Will change this to be clang resource dir later today

[anutosh491]

Hey @mcbarton I've made the change. Let me know if you have any doubts.

This basically confirms that XEUS_CPP_RESOURCE_DIR is "prefix/lib/clang/cppinterop_major_version" for all cases if not provided by the user. And for the wasm cases, we should preload these headers to /lib/clang/cppinterop_major_version from where they can be accessed.

This should be good enough to get the cppinterop ci fixed (where we just reference XEUS_CPP_RESOURCE_DIR while building)

[anutosh491]

Thanks for checking this with the relevant pr on cppinterop.

I think we're good to go !

[anutosh491]

Confident on the changes on native and wasm kernels here.

As for native, we see this in the kernelspec

  "argv": [
      "/Users/anutosh491/micromamba/envs/xeus-cpp/bin/xcpp",
      "-f",
      "{connection_file}",
      "-resource-dir", "/Users/anutosh491/micromamba/envs/xeus-cpp/lib/clang/20",
      "-I", "/Users/anutosh491/micromamba/envs/xeus-cpp/include",
      "-std=c++23"
  ]

And for wasm we see this in the kernel spec

  "argv": [
    "/Users/anutosh491/micromamba/envs/xeus-cpp-wasm-host/bin/xcpp",
    "-resource-dir", "/lib/clang/20",
    "-std=c++23"
]

Which is the exact place we are preloading the resource dir headers in the VFS (and should be accessible inside /lib/clang/20/include as shown below)