If the header isn't found, then you won't (can't) look for the library, and if the library isn't found, then the DLL won't be compiled.
What if the header is present but not an arch specific lib?
Then AC_CHECK_LIB fails.
You want enable_windows_media_speech.
I want to disable the whole DLL? that sounds odd.
Well, we usually do that on the grounds that the library isn't useful otherwise. From a completely uneducated standpoint, I can only assume that's the case here. If not, I suppose you'd want to model it after qcap and v4l2.