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/denseLM.cpp

@@ -182,7 +182,7 @@ void test_denseLM_T()
   
 }
 
-void test_denseLM()
+EIGEN_DECLARE_TEST(denseLM)
 {
   CALL_SUBTEST_2(test_denseLM_T<double>());