* ci: update Makefile

- Copied from https://github.com/samsalisbury/circleci-multi-file-config/blob/c5c5149583f7733675bb987780a5da5959450f57/copythis.circleci/Makefile

* Makefile: make ci- targets phony and more explicit

* ci: add pre-flight checks

- Right now just validates ci config is up to date.

* ci: add --skip-update-check to circleci

* ci: remove cruft from Makefile

* ci: fix missing source dir error message

* ci: consolidate circleci path handling