RFR: Add jextract guide [v6]

[Maurizio Cimadamore]

On Mon, 15 Apr 2024 13:39:03 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> doc/GUIDE.md line 306:
>> 
>>> 304: 
>>> 305: Note that for macros, jextract only generates an accessor when it sees a macro definition,
>>> 306: like the one in the example, in the header files it parses. When a macro is only defined
>> 
>> Suggestion:
>> 
>> like the one in the example, in the header files it parses. When a macro is defined
>
> `only` is relevant here. If a macro is defined using `#define` _and_ on the command line, jextract will generate an accessor.

I understand what you wanted to stress - but IMHO `only` is still redundant. E.g. "when a macro is defined using -D" is still plenty clear? Using `only` seems to convey some kind of deeper distinction e.g. that macros with -D are somehow "less macros" than the other ones. At least it's how it reads to me.

-------------

PR Review Comment: https://git.openjdk.org/jextract/pull/231#discussion_r1565866984