`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
- classify output as "not supported' also when output contains
`not supported. Stop.`, e.g. as raised by pkg/tinyusb on unsupported
CPUs / CPU families.
`add_insufficient_memory_board.sh`:
- classify output as "not supported" also when used features are
blacklisted, not only when required features are missing
- classify output as "not supported' also when output contains
`not supported. Stop.`, e.g. as raised by pkg/tinyusb on unsupported
CPUs / CPU families.
- drop all bash specifics and use generic sh
- fix all shellcheck warnings
- use nproc instead of hard-coded `-j4`
- print output on (real) compilation error
