Fix benchmarks on Raspberry Pi

[gavv]

There are two problems:

• issues when building benchmarks for ARM
• high memory usage in some benchmarks that preallocate big arrays

The goal is to build & run all benchmarks on modern RPi without swapping.

Docs:

• cross-compiling
• how to run benchmarks
• more about cross-compiling

[janibakin]

Hi! Can I work on this issue? I have Raspberry Pi 4 which I'm not using, so I could give it some purpose.

[gavv]

Thanks!