Ninja: Do not clean metadata when re-generating inside a running build

When `ninja` re-runs CMake to re-generate the build system, do not try
to use the ninja tools to update metadata on Windows.  The outer ninja
process is already holding the files open.

Issue: #20274
44 jobs for ninja-1.10
Status Job ID Name Coverage
  External
passed cdash

passed cmake-dash3win10-windows-release-ninja

passed cmake-minoc-linux-release-lint-iwyu-tidy

passed cmake-moonshade-osx-debug-ninja

passed ghostflow-check-master

passed ghostflow-stager

passed cmake-dash3win10-windows-release-ninja

00:19:49

passed cmake-dash3win10-windows-release-ninja

passed cmake-dash3win10-windows-release-ninja

passed cmake-minoc-linux-release-lint-iwyu-tidy

passed cmake-minoc-linux-release-lint-iwyu-tidy

00:05:48

passed cmake-minoc-linux-release-lint-iwyu-tidy

passed cmake-moonshade-osx-debug-ninja

00:17:54

passed cmake-moonshade-osx-debug-ninja

passed cmake-moonshade-osx-debug-ninja

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager