Pick a high level build system

[ThirteenFish]

Ninja is great as a build system, but its intended use is as a backend for a higher level system. As such it is lacking in some features one would expect - for example 7563f23 was working around the lack of lists. At some point we'll want more expressive power. I know of three candidates that use ninja as a backend:

• CMake
• Meson
• Python: ninja_syntax.py ships with Ninja.

Thoughts?