one reason to do that is some users' persistence in destroying their
non-prefix builds by trying an installation.
another reason is the fact that qt.pro's relative_qt_rpath is triggered
by the presence of an install rule for the target, which is of course
not helpful when the install dir is bogus.
Task-number: QTBUG-48406
Change-Id: I75f3940be79fcb5b86e34b975b789692423c92cb
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>
