Reduce concurrency during cmake c++ build to avoid ooms

[robert3005]

We are reaching 95% memory usage and getting oomkilled

[AdamGS]

😢

[robert3005]

going to make sure that the build succeeds before merging this

[0ax1]

2 is very low? @robert3005

[0ax1]

Does it oom bc of compiling or linking? Quite often memory usage spikes during linking.

[codspeed]

Merging this PR will degrade performance by 6.12%

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚡ 2 improved benchmarks
❌ 1 regressed benchmark
✅ 2194 untouched benchmarks
⏩ 218 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	WallTime	arrow_checked_add_u32_neon[16384]	12.3 µs	20.3 µs	-39.61%
⚡	WallTime	arrow_checked_add_u32_avx2[16384]	21.3 µs	17.6 µs	+20.77%
⚡	Simulation	allocate_drop_arrow[0]	456.9 ns	402.7 ns	+13.45%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing rk/c++flakes (8b25b38) with develop (8f3dfb4)}

Footnotes

1. 218 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[robert3005]

it's linking

[0ax1]

Superseded by: #9872. Additionally, we will intro a shared lib artefact to reduce the mem footprint during linking. In that PR, we can turn the debug info level back to 2.