Reply file names embed the configuration name verbatim. Reconfiguring
a build tree with a build type that differs from the previous one only
in case (e.g. Debug -> debug) makes CMake write a reply whose name also
differs only in case from the existing file. On a case-insensitive
filesystem the write is skipped because the name already exists, but
RemoveOldReplyFiles compared on-disk names to the just-written names
textually and deleted the surviving file, leaving the reply index
citing a target or directory reply that no longer exists on disk.
Prune reply files by file identity via cmSystemTools::GetFileId instead
of by name, so an on-disk entry that aliases a reply we just wrote is
kept. An entry whose identity cannot be obtained is retained rather
than deleted.
Fixes: #28022
e6482b840a