openmp: speedup of rbcavity by usage of multicore lib
This patch series enables openmp (https://www.openmp.org/) in the meson build and leverages a time critical part on the rbcavity program.
In the following test case
time rbcavity -d -W -r 1hp0_rdock.prm
enabling openmp on a 4 core pc brought the execution time down from
real 0m3,743s user 0m3,589s sys 0m0,097s
real 0m1,786s user 0m4,004s sys 0m0,198s
which is roughly 50% (note the slight overhead of the multicore boilerplate execution in the user time). For slower prm files and higher core counts the results should be even better.