If a header file references erasurecode_backend.h structures, it ought
to include the header file.
Note that the already-present
#ifndef _ERASURECODE_BACKEND_H_
#define _ERASURECODE_BACKEND_H_
...
#endif // _ERASURECODE_BACKEND_H_
guards ensure we don't get multiple definitions.
Change-Id: I5b8b63452b5751295cf89236693f98378f949e18
7c7373b812