Create platform plugin binary into the local plugins directory.

Set DESTDIR to $$QT.compositor.plugins/platforms in order to create
the plugin binary into the local plugins directory.  When building
Linux packages you usually are in a chroot environment and can't
write files outside your build directory, this change avoid
permission errors.

Change-Id: I3e518f20308b852f4de6a5355af60fc67681cace
Reviewed-by: Jørgen Lind <jorgen.lind@nokia.com>

src/plugins/platforms/wayland/wayland.pro

@@ -4,7 +4,7 @@ load(qt_build_config)
 
 CONFIG += link_pkgconfig qpa/genericunixfontdatabase
 
-DESTDIR = $$QT.gui.plugins/platforms
+DESTDIR = $$QT.compositor.plugins/platforms
 
 QT += core-private gui-private platformsupport-private