An incorrect backport in open-mpi/ompi#7360 removed
constants.c from ompi/mpi/fortran/use-mpi-f08/base/Makefile.am
This one off commit fixes that, and move constants.h from
ompi/mpi/fortran/use-mpi-f08 to ompi/mpi/fortran/use-mpi-f08/base
Fixesopen-mpi/ompi#7616
Signed-off-by: Gilles Gouaillardet <gilles@rist.or.jp>