Tests: Fix Plugin test include order

Fix the order accidentally broken by commit e1c77472 (Format include
directive blocks and ordering with clang-format, 2016-04-29).  Include
the KWSys header first in its own block so that it is not moved by tools
that re-order includes.  It must be included first to define large file
support macros consistently.

Tests/Plugin/src/example_exe.cxx

+#include <kwsys/DynamicLoader.hxx>
+
 #include <example.h>
 
 #include <example_exe.h>
 
 #include <iostream>
-#include <kwsys/DynamicLoader.hxx>
 #include <string>
 
 #include <stdio.h>