undef forbidden names before we #define them in case they are macros in libc

Originally committed as revision 9545 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/internal.h

@@ -234,18 +234,30 @@ if((y)<(x)){\
 #endif
 
 /* avoid usage of various functions */
+#undef  malloc
 #define malloc please_use_av_malloc
+#undef  free
 #define free please_use_av_free
+#undef  realloc
 #define realloc please_use_av_realloc
+#undef  time
 #define time time_is_forbidden_due_to_security_issues
+#undef  rand
 #define rand rand_is_forbidden_due_to_state_trashing_use_av_random
+#undef  srand
 #define srand srand_is_forbidden_due_to_state_trashing_use_av_init_random
+#undef  random
 #define random random_is_forbidden_due_to_state_trashing_use_av_random
+#undef  sprintf
 #define sprintf sprintf_is_forbidden_due_to_security_issues_use_snprintf
+#undef  strcat
 #define strcat strcat_is_forbidden_due_to_security_issues_use_av_strlcat
+#undef  exit
 #define exit exit_is_forbidden
 #if !(defined(LIBAVFORMAT_BUILD) || defined(FRAMEHOOK_H))
+#undef  printf
 #define printf please_use_av_log
+#undef  fprintf
 #define fprintf please_use_av_log
 #endif