I contributed this option to LLVM a while ago to reduce the amount of
changes clang-format makes when formatting systemd source files. As
LLVM 11 is now starting to becomes widely available, let's configure
it in the clang-format config.
The result of automatic formatting is not perfect, but if someone uses an
editor that uses that, it's probably better than nothing.
Fixes#15415.
[zjs: I resurrected this patch from #11811 and edited the extended comment
heavily.]
