Get rid of EIGEN_TEST_FUNC, unit tests must now be declared with EIGEN_DECLARE_TEST(mytest) { /* code */ }.

This provide several advantages:
- more flexibility in designing unit tests
- unit tests can be glued to speed up compilation
- unit tests are compiled with same predefined macros, which is a requirement for zapcc

unsupported/test/cxx11_tensor_thread_pool.cpp

@@ -399,7 +399,7 @@ void test_multithread_shuffle()
 }
 
 
-void test_cxx11_tensor_thread_pool()
+EIGEN_DECLARE_TEST(cxx11_tensor_thread_pool)
 {
   CALL_SUBTEST_1(test_multithread_elementwise());
   CALL_SUBTEST_1(test_multithread_compound_assignment());