Convert small static header functions to inline

Change-Id: I467b28346a0d8d4d8b96d6c05fc39c34eec26e5c

vp9/common/vp9_systemdependent.h

@@ -34,7 +34,7 @@ void vpx_reset_mmx_state(void);
 
 #if defined(_MSC_VER) && _MSC_VER < 1800
 // round is not defined in MSVC before VS2013.
-static int round(double x) {
+static INLINE int round(double x) {
   if (x < 0)
     return (int)ceil(x - 0.5);
   else