ci(cuda): limit parallel jobs to avoid OOM during CUDA build

[doringeman]

No description provided.

[sourcery-ai]

Hey - I've found 1 issue, and left some high level feedback:

• Since cmake --build already parallelizes when using Ninja, consider using CMAKE_BUILD_PARALLEL_LEVEL (or Ninja’s -j via CMAKE_BUILD_TOOL) to limit jobs instead of adding -j here, which can be less portable across generators.
• The $(nproc --ignore=2) expression assumes GNU coreutils; if these Docker builds may run on non-GNU environments, you might want to guard this or use a simpler $(nproc) with a fixed upper bound to avoid portability issues.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Since `cmake --build` already parallelizes when using Ninja, consider using `CMAKE_BUILD_PARALLEL_LEVEL` (or Ninja’s `-j` via `CMAKE_BUILD_TOOL`) to limit jobs instead of adding `-j` here, which can be less portable across generators.
- The `$(nproc --ignore=2)` expression assumes GNU coreutils; if these Docker builds may run on non-GNU environments, you might want to guard this or use a simpler `$(nproc)` with a fixed upper bound to avoid portability issues.

## Individual Comments

### Comment 1
<location path="llamacpp/native/cuda.Dockerfile" line_range="40" />
<code_context>
     -S ." > cmake-flags
 RUN cmake $(cat cmake-flags)
-RUN cmake --build build --config Release
+RUN cmake --build build --config Release -j$(nproc --ignore=2)
 RUN cmake --install build --config Release --prefix install

</code_context>
<issue_to_address>
**issue:** Guard against `nproc --ignore=2` returning 0 parallel jobs on small-core machines.

On 1–2 core machines, `nproc --ignore=2` can return 0, yielding `-j0`, which some build tools treat as unlimited parallelism or otherwise special-case. To avoid this, ensure a minimum of 1 job, e.g.:

```dockerfile
RUN cmake --build build --config Release -j"$(nproc --ignore=2 || echo 1)"
```

or use a small shell expression to compute `max(1, nproc-2)` explicitly.
</issue_to_address>

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[sourcery-ai]

issue: Guard against nproc --ignore=2 returning 0 parallel jobs on small-core machines.

On 1–2 core machines, nproc --ignore=2 can return 0, yielding -j0, which some build tools treat as unlimited parallelism or otherwise special-case. To avoid this, ensure a minimum of 1 job, e.g.:

RUN cmake --build build --config Release -j"$(nproc --ignore=2 || echo 1)"

or use a small shell expression to compute max(1, nproc-2) explicitly.

[gemini-code-assist]

Code Review

This pull request updates the cuda.Dockerfile to parallelize the CMake build process by utilizing available CPU cores. While this improves build performance, a critical issue was identified regarding the use of nproc --ignore=2, which could return a non-positive value on environments with two or fewer cores and cause the build to fail. A suggestion was provided to ensure at least one build job is always specified using a shell arithmetic check.

[gemini-code-assist]

Using nproc --ignore=2 can result in a negative or zero value if the build environment has 2 or fewer cores, causing the build command to fail. It is safer to use a shell arithmetic expansion to ensure a minimum of 1 job.

RUN cmake --build build --config Release -j$(nproc --ignore=2 | awk '{print ($1 < 1 ? 1 : $1)}')