domoticz: depends on NPTL

boost 1.66 uses pthread_condattr_setclock in
boost/asio/detail/impl/posix_event.ipp.

Boost is mostly a header-only library, in particular the asio stuff.
There are sub-options for the parts of Boost that are not purely
headers, but there are not any sub-options for the parts of Boost that
are just headers.

So, the options are either to add sub-options to Boost, or to make
Boost as a whole only available on NPTL toolchains. The latter is a bit
annoying as it would mean adding this dependency to all Boost reverse
dependencies, even those not using asio.

So, instead of updating boost, add a dependency to
BR2_TOOLCHAIN_HAS_THREADS_NPTL to domoticz. This is the best solution
that can be done today. It's not perfect, but it's good enough.

Fixes:
 - http://autobuild.buildroot.net/results/197baa15cbf7f4fc7b3ccc602515af3f375ed68f



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>