The feature of persistent collectives is approved in the Sept. 2018
MPI Forum meeting and 2018 Draft Specification of the MPI standard is
published during SC18.
Signed-off-by: KAWASHIMA Takahiro <t-kawashima@jp.fujitsu.com>
(cherry picked from commit 5f0fcf0f456aaa43f36215859412f33f79ac91f9)
Until the MPI Forum decides to add the persistent collective
communication request feature to the MPI Standard, these functions
are supported through MPI extensions with the `MPIX_` prefix.
Only C bindings are supported currently.
Signed-off-by: KAWASHIMA Takahiro <t-kawashima@jp.fujitsu.com>