Noisy warning in GPU build from Strumpack

```
70: -------------------------------------------------------
70: WARNING: SLATE is required for full GPU support.
70: SLATE is a GPU-capable replacement for ScaLAPACK, see
70:    https://github.com/icl-utk-edu/slate
70: Configure with -DTPL_ENABLE_SLATE=ON
70: and set the SLATE_DIR environment variable.
70: -------------------------------------------------------
```