accelerator_for openmp maps

[atif4461]

Data not trivially copyable and not guaranteed to be mapped correctly [-Wopenmp-mapping]
accelerator_forNB(o,mm.buffer_size/2,Merger::Nsimd,{
^~
/work/atif/Grid-BNL-HPC/Grid/threads/Accelerator.h:505:30: note: expanded from macro 'accelerator_forNB'
for ( uint64_t i=0;i<num;i++) { VA_ARGS } ;