OpenMPI nolegacylaunchers: avoid a fork bomb (#15268)

Due to the use of backquotes, the replacement script for mpirun/mpiexec commands would recursively call itself, effectively causing a fork bomb.

var/spack/repos/builtin/packages/openmpi/nolegacylaunchers.sh

@@ -3,7 +3,7 @@ echo "This version of Spack (openmpi ~legacylaunchers schedulers=slurm) "
 echo "is installed without the mpiexec/mpirun commands to prevent "
 echo "unintended performance issues. See https://github.com/spack/spack/pull/10340 "
 echo "for more details."
-echo "If you understand the potential consequences of a misconfigured `mpirun`, you can"
-echo "use spack to install `openmpi+legacylaunchers` to restore the executables."
-echo "Otherwise, use `srun` to launch your MPI executables."
+echo "If you understand the potential consequences of a misconfigured mpirun, you can"
+echo "use spack to install 'openmpi+legacylaunchers' to restore the executables."
+echo "Otherwise, use srun to launch your MPI executables."
 exit 2