RFR: Add guide section about platform-dependent nature of jextract [v2]

[Jorn Vernee]

On Wed, 17 Apr 2024 21:05:40 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Apply suggestions from code review
>>   
>>   Co-authored-by: Maurizio Cimadamore <54672762+mcimadamore at users.noreply.github.com>
>
> doc/GUIDE.md line 94:
> 
>> 92: also the section on [pre-processor definitions](#preprocessor-definitions)). Additionally,
>> 93: different built in C types can have different formats depending on the platform (for
>> 94: example, the `long` type has different formats on Linux and Windows). Both of these are
> 
> Maybe we also want to mention padding in structs?

That only really comes into play on ABIs that use a different packing (like the AIX ABI), so it doesn't really seem that important to mention. Any way, the things I mentioned are just a couple of examples. With pre-processor directives a header could really create any kind of platform dependency it wants.

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

PR Review Comment: https://git.openjdk.org/jextract/pull/237#discussion_r1570680760