Autotools: Move PHP_ODBC_* defines to configuration header

[petk]

The PHP_ODBC_* defines are remains of the PHP 2 and 3 era where the ODBC functionality was part of the PHP core and was later moved to an extension. This moves these defines to a regular PHP configuration header as done in other extensions.

Targeted after PHP-8.4.

[petk]

I've removed the PHP 9 milestone as these versions got really out of understanding what comes after 8.4. So targeting current master here. I haven't found any case where these should be added to build-defs.h header so merge coming up here sometimes soon then if everyone's fine with this.

[Girgias]

I think you are fine to merge this @petk

[petk]

Otherwise, it would be actually even better to completely remove the PHP_ODBC_{CFLAGS,LFLAGS,LIBS} but this can be done at some later version I think. Because this kind of information is not so important for the user of odbc extension and hardcodes the compile-time info into the binary making various PHP configurations (debug, release, install prefix, etc.) harder to use and install... Anyway these kind of issues some time later.