Warn in configury that the TKR 'mpi' module is deprecated

[jsquyres]

Per discussion in the 2018-10 Open MPI dev meeting:

• We probably can't remove the TKR mpi module for a while yet:
  • The NAG compiler does not support enough to utilize the ignore TKR mpi module
  • RHEL/Centos 7 uses gcc 4.8.5, and only gcc >= 4.9 has enough to support the ignore TKR mpi module
• But we thought that we could at least insert a deprecation notice for the TKR mpi module. At some point in the future we'll be able to remove it (perhaps 2020? 2021? ...?), so we might as well start warning now about removing this ancient support.
• @gpaulsen wanted to take a crack at this, so I said I'd put a note here about where he needs to look to do this work.
  • This is where we check to see if the Fortran compiler supports "ignore TKR" functionality:

    ompi/config/ompi_setup_mpi_fortran.m4

    Line 331 in 6213d23

    OMPI_FORTRAN_CHECK_IGNORE_TKR([OMPI_FORTRAN_HAVE_IGNORE_TKR=1])

  • I think that:
    1. If we are building the mpi module, and
    2. We didn't find "ignore TKR" functionality, then
    3. AC_MSG_WARN that the "TKR" mpi module is deprecated and they should upgrade their Fortran compiler.
    4. It would probably also be a good idea to OPAL_SUMMARY_ADD to get a deprecation notice also listed in the configure summary output at the end.
    5. For extra bonus points, it might also be good to have a deprecation notice in ompi_info output (!)

...speaking of which, should we have a general deprecation notices in OPAL_SUMMARY and ompi_info? E.g., for the C++ bindings and/or MPI-1 compatibility functions?

[hppritcha]

removing v4.0.x label as this definitely will not be addressed in that release.