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

test/first_aligned.cpp

@@ -26,7 +26,7 @@ void test_none_aligned_helper(Scalar *array, int size)
 
 struct some_non_vectorizable_type { float x; };
 
-void test_first_aligned()
+EIGEN_DECLARE_TEST(first_aligned)
 {
   EIGEN_ALIGN16 float array_float[100];
   test_first_aligned_helper(array_float, 50);