Crash when using MPICH

[woutersj]

When compiling against MPICH, crashes occur

Fatal error in PMPI_Gather: Invalid buffer pointer, error stack:
PMPI_Gather(403): MPI_Gather(sbuf=0x942e60, scount=80, MPI_CHARACTER, rbuf=0x942e60, rcount=80, MPI_CHARACTER, root=0, comm=MPI_COMM_WORLD) failed
PMPI_Gather(335): Buffers must not be aliased

This could be due to the use of identical recvbuf and sendbuf in MPI:
https://www.codeproject.com/Questions/1094652/Fatal-error-in-MPI-gather-matrix-multiplication-us
See also MPI_IN_PLACE:
https://www.open-mpi.org/doc/v1.8/man3/MPI_Gather.3.php#sect8

https://stackoverflow.com/questions/29415663/how-does-mpi-in-place-work-with-mpi-scatter