POSIX requires tzset(), but NuttX declared and defined it only with
CONFIG_LIBC_LOCALTIME, so programs that call it do not build without
that option. Without CONFIG_LIBC_LOCALTIME there are no time zones and
local time is UTC, so tzset() has nothing to do.
Declare tzset() always, and add an empty one for builds without
CONFIG_LIBC_LOCALTIME.
Assisted-by: Claude Code:claude-opus-5-5
Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com>
