Simplify the definition of static_vo
Simplify the definition of static_vo

For GCC, all of inline, __inline and __inline__ work fine.
For MSVC, only __inline works. (__inline should also be accepted
by RVCT.)

BelledonneCommunications/vo-amrwbenc,jiangjianping/vo-amrwbenc,jiangjianping/vo-amrwbenc,mstorsjo/vo-amrwbenc,BelledonneCommunications/vo-amrwbenc,mstorsjo/vo-amrwbenc