posix: options: add kconfig for xsi option groups

[cfriedt]

IIs your enhancement proposal related to a problem? Please describe.

Not a problem per se, but just a missing set of Kconfig options for POSIX Option Groups.

Specifically, the XSI Option Groups are not listed in Subprofiling Considerations. As a result, Zephyr does not have proper Kconfig options representing these standard Option Groups.

Encountered in the process of breaking-down #79454

Describe the solution you'd like

• Define Kconfig options for the following XSI Option Groups (-> Options)
  • (CONFIG)_XSI_CRYPT -> _XOPEN_CRYPT
  • (CONFIG)_XSI_REALTIME -> _XOPEN_REALTIME
  • (CONFIG)_XSI_ADVANCED_REALTIME -> _XOPEN_ADVANCED_REALTIME
  • (CONFIG)_XSI_REALTIME_THREADS -> _XOPEN_REALTIME_THREADS
  • (CONFIG)_XSI_ADVANCED_REALTIME_THREADS -> _XOPEN_ADVANCED_REALTIME_THREADS

The implementation should follow the existing and recent conventions added for other POSIX Option Groups - e.g. declaring constants conditionally in include/zephyr/posix/sys/sysconf.h and include/zephyr/posix/posix_features.h.

Note

Zephyr currently targets the 200809L POSIX standard, even though the latest is the 202405L standard.

Note

Since some of the XSI Option Groups mainly augment existing POSIX functionality, they might just create Kconfig definitions that select other Kconfig options.

Describe alternatives you've considered

Not creating Kconfig options for these Option Groups, although, I think that is less than ideal because it would be best to be consistent.

Additional context

• XSI_REALTIME - posix: options: add XSI_REALTIME option group #83303