Fix build on configurations without fast av_log2()

This is a bit hackish.  I will try to think of something nicer, but
this will do for now.

Originally committed as revision 22366 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/intmath.h

@@ -21,8 +21,9 @@
 #ifndef AVUTIL_INTMATH_H
 #define AVUTIL_INTMATH_H
 
+#include <stdint.h>
 #include "config.h"
-#include "common.h"
+#include "attributes.h"
 
 extern const uint32_t ff_inverse[257];
 
@@ -56,6 +57,22 @@ extern const uint32_t ff_inverse[257];
 
 #endif /* FASTDIV */
 
+/*
+ * Get definition of av_log2_c from common.h.  In the event we got
+ * here through common.h including this file, including it again will
+ * be a no-op due to multi-inclusion guards, so we must duplicate the
+ * fallback defines here.
+ */
+
+#include "common.h"
+
+#ifndef av_log2
+#   define av_log2       av_log2_c
+#endif
+#ifndef av_log2_16bit
+#   define av_log2_16bit av_log2_16bit_c
+#endif
+
 extern const uint8_t ff_sqrt_tab[256];
 
 static inline av_const unsigned int ff_sqrt(unsigned int a)