Remove split compile by default

[Kh4ster]

The split compile option has shown nondeterministic behavior. Disabling it for now.

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[coderabbitai]

📝 Walkthrough

Walkthrough

Changes

NVCC split compilation control

Layer / File(s)	Summary
Build option handling build.sh	The script accepts and documents --split-compile. The option warns about nondeterministic builds and sets NVCC_PREPEND_FLAGS to disable split compilation.
CMake compiler defaults cpp/CMakeLists.txt	Global NVCC parallel compilation retains --threads=0 without forcing --split-compile=0.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: 🟡 Moderate · up to a1d79

The default build will no longer use split compilation, but the retained opt-in path can fail on supported CUDA 12.0 environments because the option is not version-gated. Merge readiness therefore depends on guarding that path or explicitly accepting the bounded compatibility risk.

Suggested reviewers: iroy30, msarahan

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main change: disabling split compilation by default.
Description check	✅ Passed	The description explains that split compilation is disabled because it has shown nondeterministic behavior.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch remove_split_compile

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[coderabbitai]

Actionable comments posted: 1

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Inline comments:
In `@build.sh`:
- Line 17: Update build.sh’s argument validation and --split-compile handling to
reject the option when the detected CUDA version is 12.0, while preserving it
for supported CUDA versions. Add tests covering both accepted supported versions
and rejection on CUDA 12.0.

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ℹ️ Review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 03dd273 and a1d7947.

📒 Files selected for processing (2)

• build.sh
• cpp/CMakeLists.txt