Ninja: clean ninja metadata once generated
Fixes: #15830 (closed)
TODO list:
-
determine version req for the cleandead
tool (https://github.com/ninja-build/ninja/pull/1432) -
implement restat
tool (https://github.com/ninja-build/ninja/pull/1527#issuecomment-491315057) -
update ninja generator docs to suggest running these commands.