libc++ fixes: avcodec/avformat workaround

From: eroen <eroen@occam.eroen.eu>

With libc++, string includes stdint.h, which breaks the fragile avformat.h
workaround, which depends on __STDC_CONSTANT_MACROS being defined before
stdint.h is included.

Moving the string inclusion after that eyesore shouldn't break anything.
---
 apps/openmw/mwsound/ffmpeg_decoder.hpp |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/apps/openmw/mwsound/ffmpeg_decoder.hpp b/apps/openmw/mwsound/ffmpeg_decoder.hpp
index 32b2797..a5e5b50 100644
--- a/apps/openmw/mwsound/ffmpeg_decoder.hpp
+++ b/apps/openmw/mwsound/ffmpeg_decoder.hpp
@@ -1,8 +1,6 @@
 #ifndef GAME_SOUND_FFMPEG_DECODER_H
 #define GAME_SOUND_FFMPEG_DECODER_H
 
-#include <string>
-
 // FIXME: This can't be right? The headers refuse to build without UINT64_C,
 // which only gets defined in stdint.h in either C99 mode or with this macro
 // defined...
@@ -14,6 +12,8 @@ extern "C"
 #include <libavformat/avformat.h>
 }
 
+#include <string>
+
 #include "sound_decoder.hpp"