astropy.wcs.get_include() incorrect when astropy compiled against system libaries #9752

Astropy has a astropy.wcs.get_include() function for other Python packages to build against WCSLIB using the WCSLIB header files bundled with astropy (for examples where this is used see #9729 (comment)).

However at the moment the implementation of get_include() doesn't seem to take into account that astropy may have been built against a system install of WCSLIB in which case it should probably return the system headers:

https://github.com/astropy/astropy/blob/master/astropy/wcs/__init__.py#L30

Is it correct that this would need to be fixed? Or should it not matter? (we've never had reports of issues and this code has been there for a long time, so mabye in practice it's not a problem?)