Feature request: Use stdbool.h or C23 predefined constants

[schwehr]

It would be nice if we could remove some of the custom defines in cpl_serv.h. First up might be FALSE/TRUE:

https://github.com/OSGeo/libgeotiff/blob/5d5a36d858b01ed74efa786b7f76533a8ab6e997/libgeotiff/cpl_serv.h#L73-L79

Can we assume at least C99 for libgeotiff?

• <C23 - stdbool.h - https://en.cppreference.com/w/c/types
• C23 - https://en.cppreference.com/w/c/language/bool_constant

I think we can also remove NULL:

#ifndef NULL
#define NULL 0
#endif

[rouault]

Can we assume at least C99 for libgeotiff?

yes, pretty reasonable. If you want to tackle that, you're welcome

[schwehr]

It might be a while before I get to it, but I'm definitely up for doing it.