this migrates our current swift code to version 5 and 4. building is
support from 10.12.6 and xcode 9.1 onwards.
dynamic linking is the new default, since Apple removed static libs
from their new toolchains and it's the recommended way.
additionally the found macOS SDK version is printed since it's an
important information for finding possible errors now.
Fixes#6470
the force unwrapping of optionals caused many unpredictable segfaults
instead of gracefully exiting or falling back. besides that, it is bad
practice and the code is a lot more stable now.
