19156: core/compiler_hints: add likely() / unlikely() hints r=kfessel a=benpicco
19174: tests/periph_spi clearly say when init succeeds r=benpicco a=jdavid
When the `tests/periph_spi` program succeeds the output can be interpreted as an error happened.
This PR makes it clearer when it does succeed.
### Contribution description
In `tests/periph_spi`:
- Explicitely say that the init operation was successful
- Rephrase the note to avoid misinterpretations
### Testing procedure
Run the `tests/periph_spi` program.
There is not much to test, just to verify the output, should be like this:
```
2023-01-19 10:42:33,768 # Trying to initialize SPI_DEV(1): mode: 0, clk: 0, cs_port: 0, cs_pin: 0
2023-01-19 10:42:33,777 # (if below the program crashes with a failed assertion, then it means the configuration is not supported)
2023-01-19 10:42:33,779 # Success.
```
### Issues/PRs references
Issue https://github.com/RIOT-OS/RIOT/issues/19025
Co-authored-by: Benjamin Valentin <benjamin.valentin@ml-pa.com>
Co-authored-by: J. David Ibáñez <jdavid.ibp@gmail.com>
