Fix incorrect build instructions

[mcbarton]

Description

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

-DCPPINTEROP_USE_CLING=ON -DCPPINTEROP_USE_REPL=Off tells CppInterOp to use Cling in the clang-repl based instructions. Found this while working on the llvm 21 PR.

Fixes # (issue)

Type of change

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• Bug fix
• New feature
• Requires documentation updates

Testing

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Checklist

• I have read the contribution guide recently

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.83%. Comparing base (2ec0b9a) to head (7140c95).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #734   +/-   ##
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  Coverage   79.83%   79.83%           
=======================================
  Files           9        9           
  Lines        3963     3963           
=======================================
  Hits         3164     3164           
  Misses        799      799           

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[aaronj0]

These flags are unecessary as well..
Cling_DIR for sure, iirc we are no longer required to pass Clang_DIR. But thats based on how I build locally so there could be cases where it is required that I don't know of

[aaronj0]

Suggested change

	cmake -DBUILD_SHARED_LIBS=ON -DCling_DIR=$LLVM_DIR/build/tools/cling -DLLVM_DIR=$LLVM_DIR/build/lib/cmake/llvm -DClang_DIR=$LLVM_DIR/build/lib/cmake/clang -DCMAKE_INSTALL_PREFIX=$CPPINTEROP_DIR ..
	cmake -DBUILD_SHARED_LIBS=ON -DLLVM_DIR=$LLVM_DIR/build/lib/cmake/llvm -DCMAKE_INSTALL_PREFIX=$CPPINTEROP_DIR ..

[mcbarton]

@aaronj0 Thanks for the review. Good catch with the leftover Cling dir reference. Somehow I completely forgot about that. I think your right about clang_dir not being necessary. I think the cmake logic is such that as long as you pass either llvm_dir or clang_dir then it should be able to find the other. I will check this is true, and if yes, purge any reference to clang_dir from the documentation and ci so everything is consistent.