posix: features: correction on posix2 feature test macros

The _POSIX2_VERSION feature test macro should be either -1 or
left undefined on systems that do not have a POSIX-conformant
shell or utilities. Otherwise, it should be defined to the
value _POSIX_VERSION.

Since Zephyr has neither a conformant shell nor utilities, leave
_POSIX2_VERSION undefined.

Similarly, the _POSIX2_C_DEV macro should be either -1 or left
undefined if the implementation does not support the c99, lex,
and yacc shell utilities. Otherwise it should be defined to the
value _POSIX_VERSION.

Although _POSIX2_C_BIND appears to be related to the _POSIX2
family of feature test macros, all it conveys is that the
implementation supports POSIX C Language bindings, which is
always the case if the implementation uses the C programming
language, even if the implementation does not support a
conformant shell and utilities. _POSIX2_C_BIND should be
defined to the same value as _POSIX_VERSION.

Define _POSIX2_C_BIND as _POSIX_VERSION since Zephyr's
implementation of the POSIX API supports C language bindings.

The information above comes from the "unistd.h" page in the
spec and also through word search of the term "C-Language
Development Utilities".

https://pubs.opengroup.org/onlinepubs/9699919799/index.html



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