Merge topic 'FindMPI-more-robust-conditionals'

08dece8b18 FindMPI: remove unnecessary variable expansions in conditionals
1edc2f337f FindMPI: match full language names when "simplifying"
93b5bdb8b4 FindMPI: quote literal values

Acked-by: Kitware Robot <kwrobot@kitware.com>
Tested-by: buildbot <buildbot@kitware.com>
Merge-request: !7666