We need bc_compute_lib_version in CMake all of the sudden

Update to upstream version '4.4.15'
with Debian dir 203134ac244c966a4e12504903c14b4522f74785

Closes: #970747

Bump build-deps to linphone-sdk 4.4

Update to upstream version '4.4.0'
with Debian dir b1f9104ab08c65fef37cc63b02b395ecf4c87094

Update to upstream version '4.4.0~beta'
with Debian dir 28579050667e4567d08055aa975f2afb4aebd818

Update to upstream version '4.3.1'
with Debian dir 28579050667e4567d08055aa975f2afb4aebd818

Update to upstream version '4.3.0'
with Debian dir ae8078ab53ee4e9efc80813663d48c6503c23239

Downgrade a few new compiler warnings with GCC-8 for now.
These need to be investigated, but outside of the current
transition.

liblinphone9 has no rdeps beside linphone itself (which has
a strict dependency on the exact version). It uses C++ symbols
which are hard to maintain and have no gain here.

Fixes FTBFS on armel, where the signature for the C++ symbols looks
a bit different due to platform specific issues. Discussion in #d-devel
shows that these are likely leaked private symbols that can be dropped.