FindGTK2: Fix GTK2_LIBRARIES order for static gtk libraries

Before this, when creating GTK2_LIBRARIES, FindGTK2 added the GTK
dependencies in wrong order into GTK2_LIBRARIES.  With dynamic libraries
this is not a major problem, but when linking to static gtk libraries,
the linker outputs a lot of undefined symbols.  Reorder the calls that
append libraries to GTK2_LIBRARIES to respect dependency order.
Merge topic 'FindGTK2-lib-order' into next

399c3b8 FindGTK2: Fix GTK2_LIBRARIES order for static gtk libraries