Hmm, it turns out this isn't the proper fix for the issue I'm seeing, so I'll just close this.

The real problem is that `$CFLAGS` not includes `-mt_mpi` because of https://github.com/hpcugent/easybuild-framework/pull/771, and that `mpicc` picks up `$CFLAGS` and simply passes it down entirely to `icc`, including the `mt_mpi` flag (which is unknown to `icc`).  This only occurs with `ictce/4.x` though, the `mpicc` in `ictce/5.x` is smart enough not to pass down `-mt_mpi`:

```bash
bash-3.2$ module purge
bash-3.2$ module load ictce/5.5.0
bash-3.2$ mpicc -show | grep mt_mpi > /dev/null
bash-3.2$ echo $?  # -mt_mpi is *not* there
1
bash-3.2$ module purge
bash-3.2$ module load ictce/4.0.6
bash-3.2$ mpicc -show | grep mt_mpi > /dev/null
bash-3.2$ echo $?  # -mt_mpi is there
0
```