Include <math.h> or <stdlib.h> as necessary to declare functions.

Various floating-point math functions require <math.h>, and abs()
requires <stdlib.h>.

Change-Id: I6831cfdb17eac3ce129b6800f0fe82fbcfef2d28
Reviewed-on: https://code.wireshark.org/review/6002
Reviewed-by: Guy Harris <guy@alum.mit.edu>

epan/dissectors/file-mp4.c

@@ -31,6 +31,7 @@
 
 #include "config.h"
 
+#include <math.h>
 
 #include <epan/packet.h>
 #include <epan/expert.h>