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/unalignedcount.cpp

@@ -28,7 +28,7 @@ static int nb_storeu;
 
 #include "main.h"
 
-void test_unalignedcount()
+EIGEN_DECLARE_TEST(unalignedcount)
 {
   #if defined(EIGEN_VECTORIZE_AVX)
   VectorXf a(40), b(40);