Sorry, it is no longer clear to me exactly what problem(s) and solution are being proposed here.  When dealing with installation problems like this, we have to be *very* precise: here's what I started with on what platform, here are the contents of the relevant directories and/or files before I start, here are exactly the steps I took, here are the results I expected, and here are the results I observed.  Using a downloaded tarball and the steps in @yaro-yaro's initial message, I see no change in /usr/lib64; note, there *may* have been Python .so files installed there by system packages but that should be irrelevant to building and installing your own Python.  I also could not reproduce @jojo's recipe as best I understand it and don't see how it could produce any change in /usr/lib64.  Changing the value of --libdir is a whole different matter and not relevant to the original problem.  Also the title of the issue refers to DESTDIR and DESTSHARED but nowhere in the body of the issue are these variables directly referenced, so I have to assume they aren't being explicitly set.

Unless someone can better demonstrate an actual problem here, I'm going to close this issue.