In commit aebfbcaa46 (AutoGen: Use depfiles for the XXX_autogen ninja
targets, 2020-01-14, v3.17.0-rc1~58^2) the `_autogen_timestamp_deps`
target was given target ordering dependencies through its custom command
rather than direct target dependencies as on the `_autogen` target.
Then commit 895fa3433f (cmQtAutoGenInitializer: support IMPLIB-only
imported targets, 2021-09-23, v3.22.0-rc1~80^2) converted some
target-level dependencies into file-level dependencies on the custom
command. This only works with a monolithic build graph like Ninja.
Since commit ebc9e448b3 (Autogen: Add depfile support for Makefiles,
2023-09-07, v3.28.0-rc1~101^2~1) we use the `_autogen_timestamp_deps`
target in Makefile generators too. This exposed the missing target
ordering dependency.
Fixes: #25766
6193d15556