Merge topic 'ninja-many-subdirs' into release-4.0

5a36d0c9e7 Ninja: Fix regression with a large number of subdirectories
a30cf4a66a Tests/RunCMake/Configure: Split ninja-specific RerunCMake case

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !10420