gcc 4.9 has the __has_include feature which enables the
TEST_FORWARD_LIST and includes the forward_list header. This in turn
checks that the c++11 flags are enabled, or throws an error.
Change-Id: I44aa58e47c2f9ba6f14cb5a68d24da4a76698e5f
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>