19165: cpu/sam0_common: adc: implement 16 bit mode by oversampling r=dylad a=benpicco
19303: dist/tools/insufficient_memory: Minor improvements r=benpicco a=maribu
### Contribution description
`create_makefile.sh`:
- address all shellcheck warnings
- make script POSIX shell compatible
- use nproc to set the number of parallel jobs to increase throughput
- print error messages when building fails
- run `make info-boards-supported` with `EXTERNAL_BOARD_DIRS=""` to avoid adding out-of-tree boards to `Makefile.ci`.
- classify output as "not supported" also when used features are blacklisted, not only when required features are missing
`add_insufficient_memory_board.sh`:
- classify output as "not supported" also when used features are blacklisted, not only when required features are missing
### Testing procedure
Run the script; it should still work.
### Issues/PRs references
None
Co-authored-by: Benjamin Valentin <benjamin.valentin@ml-pa.com>
Co-authored-by: Marian Buschsieweke <marian.buschsieweke@ovgu.de>