Several CMake operations need to replace files in rapid succession.
This commonly fails on Windows due to filesystem lock behavior so
we have retry loops.  No matter how many times we retry or how long
we delay there will inevitably be someone with an environment that
needs more.  Make the retry count and delay configurable in the
Windows Registry keys:

 {HKCU,HKLM}/Software/Kitware/CMake/Config

in DWORD values

 FilesystemRetryCount = Number of tries
 FilesystemRetryDelay = Delay in milliseconds between tries

Leave the feature undocumented for now to see how it goes.