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/qtvector.cpp

@@ -125,7 +125,7 @@ void check_qtvector_quaternion(const QuaternionType&)
   }
 }
 
-void test_qtvector()
+EIGEN_DECLARE_TEST(qtvector)
 {
   // some non vectorizable fixed sizes
   CALL_SUBTEST(check_qtvector_matrix(Vector2f()));