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/stdvector.cpp

@@ -117,7 +117,7 @@ void check_stdvector_quaternion(const QuaternionType&)
   }
 }
 
-void test_stdvector()
+EIGEN_DECLARE_TEST(stdvector)
 {
   // some non vectorizable fixed sizes
   CALL_SUBTEST_1(check_stdvector_matrix(Vector2f()));