These global variables were instantiated in the image_sio.h header
and included into multiple translation units, violating ODR.
They are now marked as 'extern' and declared in a separate TU.
These duplicated names spanning translation units violate ODR.
They are only used within their corresponding .c files and thus
can be given static linkage.
CunrenLiang
Ryan Burns
CunrenLiang
Paul A Rosen
Eric Gurrola