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_simple.cpp

@@ -316,7 +316,7 @@ static void test_resize()
   VERIFY_IS_EQUAL(epsilon.size(), 3*5*7);
 }
 
-void test_cxx11_tensor_simple()
+EIGEN_DECLARE_TEST(cxx11_tensor_simple)
 {
   CALL_SUBTEST(test_0d());
   CALL_SUBTEST(test_1d());