The inline attribute is not valid for C standard 89. Replace the argument in the generation of header files with __inline, as well adding tests for both header files.
These new changes look good to me.
If you are updating things like this, it's often better to create a new Phab review so it's easier to see it's a new thing (or, in cases like this where the changes are simple and just test updates, they often don't need review). Either way, LGTM. Thanks for the test fix.