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

unsupported/test/EulerAngles.cpp

@@ -272,7 +272,7 @@ template<typename Scalar> void eulerangles_rand()
   check_all_var(ea);
 }
 
-void test_EulerAngles()
+EIGEN_DECLARE_TEST(EulerAngles)
 {
   // Simple cast test
   EulerAnglesXYZd onesEd(1, 1, 1);