posix: device_io: require a full libc for c89 functions

The POSIX_DEVICE_IO Option Group requires a number of c89
functions mainly from stdio.h .

Namely,

clearerr(), fclose(), feof(), ferror(), fflush(), fetc(),
fgets(), fprintf(), fputc(), fputs(), fread(), freopen(),
fscanf(), fwrite(), getc(), getchar(), gets(), perror(),
printf(), putc(), putchar(), puts(), scanf(), setbuf(),
setvbuf(), ungetc(), vfprintf(), vfscanf(), vfprintf(), and
vscanf().

These should be provided by any conformant C library
(not by the POSIX API).

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

lib/posix/options/Kconfig.device_io

@@ -8,6 +8,7 @@ config POSIX_DEVICE_IO
 	bool "POSIX device I/O [EXPERIMENTAL]"
 	select FDTABLE
 	select EXPERIMENTAL
+	select REQUIRES_FULL_LIBC
 	help
 	  Select 'y' here and Zephyr will provide an implementation of the POSIX_DEVICE_IO Option
 	  Group such as FD_CLR(), FD_ISSET(), FD_SET(), FD_ZERO(), close(), fdopen(), fileno(), open(),