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/sparseLM.cpp

@@ -168,7 +168,7 @@ void test_sparseLM_T()
       return ;
 
 }
-void test_sparseLM()
+EIGEN_DECLARE_TEST(sparseLM)
 {
   CALL_SUBTEST_1(test_sparseLM_T<double>());