message: force as c++ compiler the use of clang++ (instead of clang++-3.6) for testing MPI
diff: @@ -94,7 +94,7 @@ pipeline {
  steps {
  setupCC()
  sh "echo > make/local"
  - sh "echo CC=${env.MPICXX} -cxx=${env.CXX} >> make/local"
  + sh "echo CC=${env.MPICXX} -cxx=clang++ >> make/local"
  sh "echo STAN_MPI=true >> make/local"
  sh runTests("./")
  }
  