How to activate std::experimental::optional?

[tenspd137]

I am trying to figure out how to use the experimental::optional since I am stuck with C++14 for the time being and boost isn't an option. In the details/common.h header:

// std::experimental::optional (but not allowed in c++11 mode)
#    if defined(PYBIND11_CPP14) && (__has_include(<experimental/optional>) && \
                                 !__has_include(<optional>))
#        define PYBIND11_HAS_EXP_OPTIONAL 1
#    endif

but, is available with gcc9:

└[/usr/include/c++/9]> ls /usr/include/c++/9/optional 
/usr/include/c++/9/optional

So it isn't enabled. Is there a way to enable it that I am unaware of?

Thanks!