Explicitly defaulted move assignment operator is implicitly deleted

[Kronuz]

• Compiler Used: Clang 8.0.0 (tags/RELEASE_800/final)
• Operating System: macOS Mojave
• Architecture (ARM/x86/32bit/64bit/etc): x86_64

Expected Behavior

Compile without warnings.

Actual Behavior

I'm getting:

chaiscript/dispatchkit/../language/chaiscript_common.hpp:731:25: warning: explicitly defaulted move assignment operator is implicitly deleted [-Wdefaulted-function-deleted]
        Stack_Push_Pop& operator=(Stack_Push_Pop &&) = default;
                        ^
chaiscript/dispatchkit/../language/chaiscript_common.hpp:748:53: note: move assignment operator of 'Stack_Push_Pop' is implicitly deleted because field 'm_ds' is of reference type 'const chaiscript::detail::Dispatch_State &'
          const chaiscript::detail::Dispatch_State &m_ds;

and others of the like.

Minimal Example to Reproduce Behavior

Just compile any example with Clang 8