Creating a `Symbol` with `type = SYM_LABEL` but `section = nullptr`
is inconsistent and dangerous. I was not able to cause any buggy
behavior so far, but it's safer and reasonable to not create such
a symbol in the first place.
The main consequence is that `DEF(LabelOutsideSection)` will now
evaluate as 0.
- "Double quotes" for strings (filenames, section names, CLI option arguments, etc)
- 'Single quotes' for characters and CLI option flags
- `Backticks` for keywords and identifiers (symbol names, charmap names, etc)
CLI option flags also have their leading dashes
POSIX leaves undefined the order of output if stderr is injected into stdout,
and in practice it differs on Windows (Linux buffers both streams separately,
Windows interleaves them as they arrive without buffering).
This should help testing on other platforms