Correct, portable definition of INT_BIT

Originally committed as revision 17480 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/internal.h

@@ -88,11 +88,7 @@
 #endif
 
 #ifndef INT_BIT
-#    if INT_MAX != 2147483647
-#        define INT_BIT 64
-#    else
-#        define INT_BIT 32
-#    endif
+#    define INT_BIT (CHAR_BIT * sizeof(int))
 #endif
 
 #if ( defined(__PIC__) || defined(__pic__) ) && ! defined(PIC)