The Debug Libraries installer can be found from its info page: http://download.qt-project.org/official_releases/qt/4.8/4.8.5/qt-mac-opensource-4.8.5-debug-libs.dmg.mirrorlist
When the DMG is opened, and the Qt_debuglibraries.pkg file is run, the installer should show the major and minor version numbers. Instead, it shows:
A screenshot is attached to illustrate. This does not affect the installation in any adverse way.