Build dependencies from Unix directories

Here is a problematic but common scenario:

• We have a normal installation of a product X in a Unix directory. This is used by our builds. No mention of the files used is recorded in the config records of the derived objects produced: with respect to these files, clearmake behaves exactly as the standard make and relies fully on time stamps.
• We install a new version of X. A large number of the files are upgraded so that neither their name nor their path changes. We build with clearmake: only the DOs whose time-stamp was older than this of the files in the new version are rebuilt. From ClearCase's point of view, the others are valid! In order to be sure, we can resort to building "unconditional".
• We get a customer report and want to build a bug fix. We may have left one host with a local installation of the previous version of X --which was used-- or we may uninstall the new version and reinstall the old (on one host). Again, a normal build will not detect the change and will validate at least for some DOs, the files produced with the other version of X! At this point, and later as we switch back to the new version, the only recourse for use is to build unconditional: otherwise clearmake may winkin versions of either set!
  We can make a careful analysis and remove one set of DOs. Also, eventually the problem will fade away as we edit our sources and compile them in the appropriate environment.

The problem comes indeed from the fact that ClearCase maintains several versions of the DOs, which other SCM tools typically don't do.