add config option to use dynamic arch when available?

[migueldiascosta]

following up on easybuilders/easybuild-easyconfigs#2066

OpenBLAS can be built with dynamic arch, i.e., built for multiple instruction sets that can be dynamically selected according to the capabilities of the execution node and, eventually, via environment variables.

This is not how OpenBLAS has been traditionally used with EasyBuild, but it is how Intel MKL is distributed, it's just that in that case we don't have a choice on how it is built.

For sites that already build for multiple architectures it's largely irrelevant but there are other use cases, for instance a "slightly heteregeneous" cluster where for some reason one would want to maintain a single tree but still be able to take advantage of the "free" speedup from dynamic arch on math libraries (as is already the case with Intel MKL...)

This can of course already be done at many different levels of site customization, but having a dedicated EB option (and checking it in the easyblock) would allow setting this preference globally without affecting any other behaviour (e.g. optarch).

This would make additional sense if there are other libraries/applications where it could be used, I don't know if there are...

Thoughts?

[truatpasteurdotfr]

gromacs can be tuned at build time with the GMX_SIMD flag (http://manual.gromacs.org/current/install-guide/index.html#simd-support)