romio: redefine MPI_DISPLACEMENT_CURRENT

[hzhou]

Pull Request Description

It is quite odd to have -54278278 for MPI_DISPLACEMENT_CURRENT let users and developers wonder its reasons. In fact, I believe this is used as a sentinel dummy argument and an arbitary value should work.

The value -1 is as arbitrary as -54278278 and people won't wonder.

Author Checklist

• Provide Description
  Particularly focus on why, not what. Reference background, issues, test failures, xfail entries, etc.
• Commits Follow Good Practice
  Commits are self-contained and do not do two things at once.
  Commit message is of the form: module: short description
  Commit message explains what's in the commit.
• Passes All Tests
  Whitespace checker. Warnings test. Additional tests via comments.
• Contribution Agreement
  For non-Argonne authors, check contribution agreement.
  If necessary, request an explicit comment from your companies PR approval manager.

[hzhou]

test:mpich/ch3/tcp

test:mpich/custom
config: mpi-abi

Somehow cvars such as MPIR_CVAR_ALLTOALLW_INTRA_ALGORITHM is not set properly with abi and the new testing framework. But the IO tests seems fine.

[hzhou]

test:mpich/custom
config: mpi-abi

[raffenet]

Tests look OK with this value. Should be propose a change to https://github.com/mpi-forum/mpi-standard/pull/977 for next week's second vote?

[hzhou]

I am for it

[hzhou]

Let me drop the last commit (05c3ec9) and test. If test pass, it means we can maintain both MPICH ABI and whatever negative value MPI ABI will use.

[hzhou]

test:mpich/custom
config: mpi-abi
✔️

[hzhou]

test:mpich/ch3/tcp ✔️
test:mpich/ch4/ofi

[dalcinl]

@raffenet @hzhou Could you please bump priority to the review & merge of this PR? mpi4py's MPI ABI testing requires the MPI ABI stubs header and MPICH's MPI ABI implementation in sync.