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/dontalign.cpp

@@ -44,7 +44,7 @@ void dontalign(const MatrixType& m)
   internal::aligned_delete(array, rows);
 }
 
-void test_dontalign()
+EIGEN_DECLARE_TEST(dontalign)
 {
 #if defined EIGEN_TEST_PART_1 || defined EIGEN_TEST_PART_5
   dontalign(Matrix3d());