Optimizations for Fugaku: Pinning, Compile flags

[krenzland]

Draft: Needs to be merged with master, new pinning routines need to be checked on other clusters.

This PR adds changes needed to run on Fugaku. This includes adding support for NUMA aware pinning in cases when CPU cores are deactivated using the hot-plugging system of Linux: https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-devices-system-cpu

[Thomas-Ulrich]

LGTM

[davschneller]

As a note: I tried this one out on LUMI as well—but it didn't show any offline cores there.

However, lstopo shows the usual 7 CPUs (instead of 8). ... Maybe long-term it would be even of use to implement hwloc support?

[davschneller]

Even though this branch should be kind of ready, it's probably better to wait at least until the training next week is over before merging it (the area it modifies may cause trouble with Mac OS systems—if there's some preprocessor guard missing somewhere).