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/unalignedassert.cpp

@@ -174,7 +174,7 @@ void unalignedassert()
 #endif
 }
 
-void test_unalignedassert()
+EIGEN_DECLARE_TEST(unalignedassert)
 {
   CALL_SUBTEST(unalignedassert());
 }