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/exceptions.cpp

@@ -107,7 +107,7 @@ void memoryleak()
   VERIFY(ScalarWithExceptions::instances==0 && "global memory leak detected in " && EIGEN_MAKESTRING(OP)); \
 }
 
-void test_exceptions()
+EIGEN_DECLARE_TEST(exceptions)
 {
   CALL_SUBTEST( memoryleak() );
 }