Support spectrum MPI

[pakmarkthub]

The name of spectrum MPI library is libmpi_ibm.so, not the standard libmpi.so. Although the MPI API libgdsync uses are compatible with spectrum MPI, configure hard-codes the link library with -lmpi. Hence, it cannot be built.

WAR: Users can always edit Makefile.am and changes -lmpi to -lmpi_ibm. But it would be better if the script can detect and change automatically.