Install targets and files in default Runtime and Development CMake
components to determine files included in the two Debian packages.
Move to CMake minimum version to 3.12 to allow using NAMELINK_COMPONENT
option in install() allowing adding .so files in a separate component,
Developement here.
Use CPack to build the two Debian packages.

Consider the ful package delivers the two libraries wiringPi and
wiringPiDev with the associated binary gpio. We don't have to build and
install each component separately first.

CMake configuration will fail if not found instead of waiting for build.