add multiple inclusion guards to headers

Originally committed as revision 9345 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/armv4l/mathops.h

@@ -19,6 +19,9 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#ifndef AVCODEC_ARM_MATHOPS_H
+#define AVCODEC_ARM_MATHOPS_H
+
 #ifdef FRAC_BITS
 #   define MULL(a, b) \
         ({  int lo, hi;\
@@ -47,3 +50,5 @@
          __rt; })
 
 #endif
+
+#endif