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/num_dimensions.cpp

@@ -60,7 +60,7 @@ using TMatrix = Matrix<Scalar,Rows,Cols>;
 
 #endif
 
-void test_num_dimensions()
+EIGEN_DECLARE_TEST(num_dimensions)
 {
   int n = 10;
   ArrayXXd A(n,n);