Since commit f50fb77a4f (Ninja: Regenerate when test or install scripts
are missing, 2024-10-29, v4.0.0-rc1~516^2) the list of paths we pass to
`ninja -t restat` scales with the number of project subdirectories.
Run it in blocks to avoid "command line too long" errors, particularly
on Windows.
Fixes: #26738
