Defining spaceship operators for glm types

[alexanderbock]

We use glm in our project extensively and have recently added the new spaceship operator to our classes, for example:

    struct CameraNavState {
        static constexpr std::string_view Type = "setNavigationState";

        std::string anchor;
        std::optional<std::string> aim;
        std::string referenceFrame;
        glm::dvec3 position;
        std::optional<glm::dvec3> up;
        std::optional<double> yaw;
        std::optional<double> pitch;

        auto operator<=>(const CameraNavState&) const = default;
    };

while MSVC is totally happy with this, for Clang17 this results in a warning:

/OpenSpace/include/openspace/scene/profile.h:143:14: warning: explicitly defaulted three-way comparison operator is implicitly deleted [-Wdefaulted-function-deleted]
  143 |         auto operator<=>(const CameraNavState&) const = default;
      |              ^
/OpenSpace/include/openspace/scene/profile.h:138:20: note: defaulted 'operator<=>' is implicitly deleted because there is no viable three-way comparison function for member 'position'
  138 |         glm::dvec3 position;
      |                    ^
/OpenSpace/include/openspace/scene/profile.h:143:57: note: replace 'default' with 'delete'

Is there a CMake flag that I'm missing to set that already would enable this? I went through the header and didn't find it, but it seems to me as if enough operators are defined for the compiler to be able to automatically synthesize the spaceship. Alternatively, would it be possible to add that definition to the types?