- remove redundant loop when reuniting outputs from all threads

- For safety, since some loops are murky, overallocate some arrays of size nspheres instead of configurations
- correct a race in the definition of myompthread
- add some omp barriers to force synchronisations

Merge branch 'test_omp_cluster' of https://www.ict.inaf.it/gitlab/giacomo.mulas/np_tmcode into test_omp_cluster
Update make.inc to use OMP

Move the content of the loop over scales in a separate function, so it can be called with fresh arguments every time to check parallelism and dependencies.

- turn C4 from a structure to a class (to do the above), move its initialisation to its constructor
- eliminate "allocate_vectors()", redundant and including a (wrong) double allocation

Always refer to np_int definition

See merge request giacomo.mulas/np_tmcode!25

Link with LAPACKe

See merge request giacomo.mulas/np_tmcode!24