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/determinant.cpp

@@ -50,7 +50,7 @@ template<typename MatrixType> void determinant(const MatrixType& m)
   VERIFY_IS_APPROX(m2.block(0,0,0,0).determinant(), Scalar(1));
 }
 
-void test_determinant()
+EIGEN_DECLARE_TEST(determinant)
 {
   for(int i = 0; i < g_repeat; i++) {
     int s = 0;