Renamed ocl tests' precomp files according to convention.

Also, added the missing include guard to perf_precomp.hpp.
This should fix the build.

modules/ocl/test/test_sort.cpp

@@ -44,7 +44,7 @@
 //M*/
 #include <map>
 #include <functional>
-#include "precomp.hpp"
+#include "test_precomp.hpp"
 
 using namespace std;
 using namespace cvtest;