thread in contiguous place partitions.  And with 'SPREAD' a sparse
     distribution across the place partitions is used.  Specifying more
     than one item in the list will automatically enable nesting by
     default.

     When undefined, 'OMP_PROC_BIND' defaults to 'TRUE' when
     'OMP_PLACES' or 'GOMP_CPU_AFFINITY' is set and 'FALSE' otherwise.

_See also_:
     *note omp_get_proc_bind::, *note GOMP_CPU_AFFINITY::, *note
     OMP_NESTED::, *note OMP_PLACES::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 4.4