cmQtAutoGenInitializer: support IMPLIB-only imported targets

Instead of using the target name directly (which ends up in the `Ninja`
generators querying for the `LOCATION` parameter), wrap up the target
name in a `$<TARGET_LINKER_FILE:>` to avoid the query for the unset
property.
48 jobs for !6558 with autogen-dep-on-imported-implib-only-target in 62 minutes and 37 seconds (queued for 1 second)
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