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/redux.cpp

@@ -146,7 +146,7 @@ template<typename VectorType> void vectorRedux(const VectorType& w)
   VERIFY_RAISES_ASSERT(v.head(0).maxCoeff());
 }
 
-void test_redux()
+EIGEN_DECLARE_TEST(redux)
 {
   // the max size cannot be too large, otherwise reduxion operations obviously generate large errors.
   int maxsize = (std::min)(100,EIGEN_TEST_MAX_SIZE);