Files which are installed as-is (any .service and other unit files, .conf
files, .policy files, etc), are left as is. My assumption is that SPDX
identifiers are not yet that well known, so it's better to retain the
extended header to avoid any doubt.
I also kept any copyright lines. We can probably remove them, but it'd nice to
obtain explicit acks from all involved authors before doing that.
The fuzzers will be used by oss-fuzz to automatically and
continuously fuzz systemd.
This commit includes the build tooling necessary to build fuzz
targets, and a fuzzer for the DNS packet parser.
