package/chrony: bump to version 4.7
Release notes: https://chrony-project.org/news.html
Since this release, building without POSIX threads is no longer supported.
So add a depends on BR2_TOOLCHAIN_HAS_THREADS.
Signed-off-by: Scott Fan <fancp2007@gmail.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>