[None][fix] Propagate NCCL_INCLUDE_DIR to common header dirs

[lucifer1004]

When building against a custom NCCL via --nccl_root (e.g. the pip nvidia-nccl-cu13 wheel, whose headers do not live in a compiler default path), FindNCCL resolves NCCL_INCLUDE_DIR correctly but the directory is never added to the compile include paths — multi-device translation units then fail with nccl.h: No such file or directory even though configure succeeded.

Append NCCL_INCLUDE_DIR to COMMON_HEADER_DIRS when ENABLE_MULTI_DEVICE is on. No behavior change for builds whose NCCL headers already sit in default include paths.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Fixed multi-device builds so components can locate the NCCL header when the NCCL include directory is configured.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 6929451 and b251f8c.

📒 Files selected for processing (1)

• cpp/CMakeLists.txt

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📝 Walkthrough

Walkthrough

The CMake configuration now appends NCCL_INCLUDE_DIR to COMMON_HEADER_DIRS when multi-device support is enabled and the directory is available, allowing targets to locate nccl.h without directly linking NCCL::nccl.

Changes

Multi-device build configuration

Layer / File(s)	Summary
Propagate NCCL include path cpp/CMakeLists.txt	When ENABLE_MULTI_DEVICE is enabled and NCCL_INCLUDE_DIR is set, the build adds that directory to COMMON_HEADER_DIRS for nccl.h discovery.

Estimated code review effort: 1 (Trivial) | ~3 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description explains the issue and fix, but it omits the required Test Coverage and PR Checklist sections.	Add a Test Coverage section and complete the PR Checklist items, or clearly mark any non-applicable items.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title matches the main change and follows the repository's required [None][fix] format.
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.

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