v4.1.x: coll/ucc: add reduce scatter block#12897

jsquyres merged 1 commit intoopen-mpi:v4.1.xopen-mpi/ompi:v4.1.xfrom

Sergei-Lebedev:topiv/v4.1.x_ucc_rs_blockSergei-Lebedev/ompi:topiv/v4.1.x_ucc_rs_blockCopy head branch name to clipboard