Fixes #4785: Move r32217 to v1.8 branch (oshmem: fix warnings)

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r32217 [[BR]]
oshmem: fix warnings

fixed by Igor, reviewed by Miked

cmr=v1.8.2:reviewer=ompi-rm1.8
Fixes #4764: Move r31524, r32139, r32140, r32213 to v1.8 branch (Fix a cornercase with MPI_PROC_NULL)

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r31524 [[BR]]
Fix the issue reported by Gilles Gouaillardet regarding the
MPI_PROC_NULL persistent requests.

r32139 [[BR]]
Fix the cornercase with MPI_PROC_NULL persistent requests.

This corner case is now handled in the pml so the same code
is invoked for both MPI_Start and MPI_Startall.
This also correctly report an error if MPI_Startall is invoked twice
on a MPI_PROC_NULL persistent request.

r32140 [[BR]]
Cleanup : fix the cornercase with MPI_PROC_NULL persistent requests.

r32213 [[BR]]
Fix a cornercase with MPI_PROC_NULL persistent requests

Handle OMPI_REQUEST_NOOP in MPI_Startall rather than PML

cmr=v1.8.2:reviewer=bosilca:ticket=4764