message: Allow either openmpi or mpich in Jenkinsfile.
diff: @@ -91,8 +91,12 @@ pipeline {
  }
  stage('Non-windows interface tests with MPI') {
  agent { label 'linux' }
  + environment {
  + OMPI_CXX = "${env.CXX}"
  + MPICH_CXX = "${env.CXX}"
  + }
  steps {
  - setupCC("${env.MPICXX} -cxx=${env.CXX}")
  + setupCC("${env.MPICXX}")
  sh "echo STAN_MPI=true >> make/local"
  sh "make build-mpi > build-mpi.log 2>&1"
  sh runTests("./")
  