Propagating usage of check_c_source_compiles instead of check_function_exists in MPI tests
Propagating usage of check_c_source_compiles instead of check_function_exists in MPI tests

mcopik/Elemental,mcopik/Elemental,birm/Elemental,mcopik/Elemental,justusc/Elemental,justusc/Elemental,birm/Elemental,mcopik/Elemental,birm/Elemental,mcopik/Elemental,birm/Elemental,justusc/Elemental,justusc/Elemental,birm/Elemental,justusc/Elemental,justusc/Elemental,mcopik/Elemental,birm/Elemental