Compilation fails on platforms where sizeof(long double) == sizeof(double)

[ursg]

Specifically, I tested on armv7l (raspberryPi 3), and got:

mpic++ -O3 -std=c++0x -Wall -fPIC  -c vlsv_common_mpi.cpp
vlsv_common_mpi.cpp: In function ‘ompi_datatype_t* vlsv::getMPIDatatype(datatype::type, uint64_t)’:
vlsv_common_mpi.cpp:159:11: error: duplicate case value
  159 |           case (sizeof(long double)):
      |           ^~~~
vlsv_common_mpi.cpp:155:11: note: previously used here
  155 |           case (sizeof(double)):
      |           ^~~~
make: *** [Makefile:67: vlsv_common_mpi.o] Error 1

Not sure if this is something that needs a specific fix though. This issue is mostly to document it, if anybody stumbles into this in the future. Most likely, it can be worked around by simply commenting out the long double case, as it is not used for any actual application AFAIK.

[iljah]

Could instead use if (sizeof(float)) {} else if (sizeof(double)) {} else if (sizeof(long double)) {}...