posix: sys: sysconf: Unconditionally define POSIX macros

The POSIX macros PAGE_SIZE and PAGESIZE (queriable through
sysconf()) were conditionally defined only if an existing definition
did not already exist. These should be defined unconditionally in their
header to ensure they get the correct values.

If these macros are defined elsewhere with a different meaning, that's a
problem. There was an issue where PAGESIZE was already defined with a
different meaning. See zephyrproject-rtos#74623 and zephyrproject-rtos#74428.

The POSIX macro ATEXIT_MAX is also conditionally defined and should be
unconditionally defined, but there is currently a definition in picolibc
(picolibc/newlib/libc/include/stdlib.h) so this change will be done
separately.

This commit defines PAGE_SIZE and PAGESIZE unconditionally.

Signed-off-by: Ben Marsh <[email protected]>

include/zephyr/posix/posix_features.h

@@ -314,13 +314,8 @@
 #define ATEXIT_MAX 8
 #endif
 
-#ifndef PAGE_SIZE
 #define PAGE_SIZE CONFIG_POSIX_PAGE_SIZE
-#endif
-
-#ifndef PAGESIZE
 #define PAGESIZE PAGE_SIZE
-#endif
 
 #define PTHREAD_DESTRUCTOR_ITERATIONS _POSIX_THREAD_DESTRUCTOR_ITERATIONS
 #define PTHREAD_KEYS_MAX              _POSIX_THREAD_KEYS_MAX