install .lib files for static libs again

the no_dll switch has questionable semantics: it pro-actively breaks
non-dll builds. therefore its usage needs to be limited to dll build.

Task-number: QTBUG-39594
Change-Id: I98328e502693df835af565b5ec25ada2c1c168ad
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

mkspecs/features/qt_installs.prf

@@ -22,7 +22,7 @@
         target.path = $$[QT_HOST_LIBS]
     else: \
         target.path = $$[QT_INSTALL_LIBS]
-    target.CONFIG = no_dll
+    !static: target.CONFIG = no_dll
     INSTALLS += target
 }