Cmake and meson project support

[mattiasb]

Add support for building and testing CMake- and Meson projects.

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Before submitting a PR make sure the following things have been done (and denote this
by checking the relevant checkboxes):

• [✓] The commits are consistent with our contribution guidelines
  • With caveat that this PR adds support for two similar project types in one go. I can easily split this up if wanted.
• [✓] You've added tests (if possible) to cover your change(s)
  • Does not apply I believe (?)
• [✓] All tests are passing (make test)
• [✓] The new code is not generating bytecode or M-x checkdoc warnings
  • Not the new code no.
• [✓] You've updated the changelog (if adding/changing user-visible functionality)
• [✓] You've updated the readme (if adding/changing user-visible functionality)
  • Not applicable

Thanks!

[bbatsov]

👍