Investigate a clear way to notify developers when TPLs need to be rebuilt

[white238]

It is unclear to developers that TPLs need to be rebuilt when they are updated by others on the team. We should investigate a solution to this so that people don't waste time wondering when their code fails to build.

Possible suggestions (per @samuelpmishLLNL) :

• Pull version number out to its own variable in host-config (ie SERAC_AXOM_VERSION) which then gets used in both AXOM_DIR and an internal check at the CMake stage

[joshessman-llnl]

In my experience this is most frequently a problem with TPLs for which we track hashes; it would be useful if Spack let us use commit SHAs as versions such that the library would be installed to a directory contained the commit hash. In that case it'd be fairly easy to detect a mismatch since many libraries (including axom) don't write their Git hash to CMake config files.