demo projects don't build

[pptz]

Ubuntu 16. The problem during cmake stage is:

CMake Warning (dev) at CMakeLists.txt:18 (add_executable):
Policy CMP0028 is not set: Double colon in target name means ALIAS or
IMPORTED target. Run "cmake --help-policy CMP0028" for policy details.
Use the cmake_policy command to set the policy and suppress this warning.

Target "raw" links to target "Threads::Threads" but the target was not
found. Perhaps a find_package() call is missing for an IMPORTED target, or
an ALIAS target is missing?
This warning is for project developers. Use -Wno-dev to suppress it.

And building will fail.

The solution is to add to CMakeLists.txt:

set(THREADS_PREFER_PTHREAD_FLAG ON)
find_package(Threads REQUIRED)

For more: https://stackoverflow.com/questions/1620918/cmake-and-libpthread