Use standard C for implementing sign_extend() and zero_extend().

This fixes compilation of probetest

Originally committed as revision 23116 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mathops.h

@@ -118,14 +118,14 @@ static inline av_const int mid_pred(int a, int b, int c)
 #ifndef sign_extend
 static inline av_const int sign_extend(int val, unsigned bits)
 {
-    return (val << (INT_BIT - bits)) >> (INT_BIT - bits);
+    return (val << ((8 * sizeof(int)) - bits)) >> ((8 * sizeof(int)) - bits);
 }
 #endif
 
 #ifndef zero_extend
 static inline av_const unsigned zero_extend(unsigned val, unsigned bits)
 {
-    return (val << (INT_BIT - bits)) >> (INT_BIT - bits);
+    return (val << ((8 * sizeof(int)) - bits)) >> ((8 * sizeof(int)) - bits);
 }
 #endif