Remove C++ struct calling convention hack and fix bug masked by it

[jrtc27]

This hack causes the C and C++ calling conventions for small structs containing capabilities to differ and thus breaks code passing such structs across the language barrier.

[arichardson]

Thanks! Only minor comment I have is to maybe add a commit first that autogenerates the check lines so that the bugfix commit highlights the change in the IR.

[jrtc27]

Thanks! Only minor comment I have is to maybe add a commit first that autogenerates the check lines so that the bugfix commit highlights the change in the IR.

Yeah that's a good suggestion, now done.