Mirror the behavior in unixmake.cpp and do actually install
/uninstall files in target.targets. This fixes the installation of
.debug files on MinGW for a Qt with -force-debug-info
-separate-debug-info.
[ChangeLog][qmake] Install/uninstall rules are now generated for
target.targets on Windows. This mirrors the behavior on Unix.
Fixes: QTBUG-81354
Change-Id: Ie9366f132ebd8e18680f32f2e52cec64dbd87e9a
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>