posix: do not rely on PAGE_SIZE being defined in limits.h

Since an implementation may omit definitions of runtime invariant values
in limits.h if the corresponding value is equal to or greater than the
minimum, is unspecified, and must be queried at runtime [1], do not rely
on PAGE_SIZE being declared in limits.h .

[1]
https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/limits.h.html



Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>