Since in next commit osmo-trx-lms starts using smpl_buf.cpp, it seems
some automake step doesn't like including a cpp file twice from a
different directory, since race conditions can occur building it.
Instead we define the dependency by first building a static lib and then
using it on each libdevice.la (one per device type).
We already do the similar under arch/ subdir, where we have a common/
subdir and then one subdir and lib per architecture.
Change-Id: I465ad0f6d5569bb3006d711c8fd0df14391fcf35
Pau Espin