Starting from MPI standard 3.0, MPI_Count and 4.0 MPI_xxx_c APIs have been
added to support large (> 2^31-1) datatypes. This PR checks the availability of
those large count MPI APIs and if they are implemented in the underlying MPI
library, then they will be used to create large datatype for fileview and user
buffer datatypes. This way, we can support large single requests by calling
the same MPI_File_read/write APIs whose count argument is still of type int.
This PR thus deprecates the configure option --enable-large-single-req
Starting from MPI standard 3.0, MPI_Count and 4.0
MPI_xxx_cAPIs have been added to support large (> 2^31-1) datatypes. This PR checks the availability of those large count MPI APIs and if they are implemented in the underlying MPI library, then they will be used to create large datatype for fileview and user buffer datatypes. This way, we can support large single requests by calling the same MPI_File_read/write APIs whose count argument is still of typeint.This PR thus deprecates the configure option --enable-large-single-req