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/sparse_ref.cpp

@@ -126,7 +126,7 @@ void call_ref()
   VERIFY_EVALUATION_COUNT( call_ref_5(A.row(2), A.row(2).transpose()),  1);
 }
 
-void test_sparse_ref()
+EIGEN_DECLARE_TEST(sparse_ref)
 {
   for(int i = 0; i < g_repeat; i++) {
     CALL_SUBTEST_1( check_const_correctness(SparseMatrix<float>()) );