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/nomalloc.cpp

@@ -202,7 +202,7 @@ template<typename MatrixType> void test_reference(const MatrixType& m) {
 
 }
 
-void test_nomalloc()
+EIGEN_DECLARE_TEST(nomalloc)
 {
   // create some dynamic objects
   Eigen::MatrixXd M1 = MatrixXd::Random(3,3);