Fix for compilation with newer ffmpeg library

Error was cased by undefined UINT64_C in stdint.h for c++
programs. As I understand from ffmpeg mailing list the simpliest
solution is to define __STDC_CONSTANT_MACROS before including
ffmpeg libraries. There already was some amout of such definitions in
the code and I've tested this with newer and older ffmpeg
libraries -- this should work and should be safe, but maybe
there is better way of fixing this problem.

intern/audaspace/ffmpeg/AUD_FFMPEGFactory.cpp

@@ -23,6 +23,9 @@
  * ***** END LGPL LICENSE BLOCK *****
  */
 
+// needed for INT64_C
+#define __STDC_CONSTANT_MACROS
+
 #include "AUD_FFMPEGFactory.h"
 #include "AUD_FFMPEGReader.h"
 #include "AUD_Buffer.h"

intern/audaspace/intern/AUD_C-API.cpp

@@ -27,6 +27,11 @@
 #include <cstring>
 #include <cmath>
 
+#ifdef WITH_FFMPEG
+// needed for INT64_C
+#define __STDC_CONSTANT_MACROS
+#endif
+
 #include "AUD_NULLDevice.h"
 #include "AUD_I3DDevice.h"
 #include "AUD_FileFactory.h"
@@ -62,6 +67,7 @@
 #include "AUD_JackDevice.h"
 #endif
 
+
 #ifdef WITH_FFMPEG
 extern "C" {
 #include <libavformat/avformat.h>

intern/audaspace/intern/AUD_FileFactory.cpp

@@ -29,6 +29,9 @@
 #include <cstring>
 
 #ifdef WITH_FFMPEG
+// needed for INT64_C
+#define __STDC_CONSTANT_MACROS
+
 #include "AUD_FFMPEGReader.h"
 #endif
 #ifdef WITH_SNDFILE