Here's an even less ugly new version of the patch; it does everything with multi-byte strings instead of wide-char strings (so that there's just one conversion of prefix from wcs to mbs at the beginning of the block, and TCL_VERSION is used directly).  This patch also cleans up the Tkinter tests to remove the previous workarounds and un-reverts the change to PCbuild/rt.bat that I reverted after #15968 in an attempt to avoid test failures (that apparently didn't work).