ENH add systemd-devel

[mbargull]

Please see the repo readme for directions on how to make PRs on this repo.

Checklist:

• [x] if you have added a CDT, it appears in the cdt_slugs.yaml file and you have rerun the script python gen_cdt_recipes.py.
• [ ] if you have changed the CDT generator code (rpm.py), you have bumped the build number in conda_build_config.yaml and have remade all of the recipes via running python gen_cdt_recipes.py --force
• [ ] if you have added a custom CDT recipe, you have added the name of the CDT with custom: true in the cdt_slugs.yaml file.
• [x] all CDT recipes have build number set by {{ cdt_build_number }} for old-style/legacy CDTs or {{ cdt_build_number|int + 1000 }} for new-style CDTs
• [x] if you see a warning about a CDT not having a license, you have added the license_file key in the cdt_slugs.yaml file with the path to the appropriate license in licenses/

NOTE: If you make any changes to cd_slugs.yaml, you need to reun the generator code via python gen_cdt_recipes.py. Add the --fast option to make this go more quickly.

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Forgot this one in gh-36.

[mbargull]

Adding this for completeness' sake. But I won't use that myself, actually :/. I wanted the CDTs for v201/src/systemd/sd-bus.h which I thought was included because CentOS 7 ships v219, but apparently it's only available from v221 onward <-- that I only noticed afterwards... bummer!