lavc/audiotoolboxdec: fix OSX SDK detection

__MAC_10_11 can be present in updated revision of an older SDK so it
can't reliably detect availability of kAudioFormatEnhancedAC3 constant.

Fixes: b4daa2c40f ('lavc/audiotoolboxdec: add eac3 decoder')
Cc: Rodger Combs <rodger.combs@gmail.com>
Signed-off-by: Dmitry Kalinkin <dmitry.kalinkin@gmail.com>
Previous version reviewed by: Rodger Combs <rodger.combs@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/audiotoolboxdec.c

@@ -32,7 +32,7 @@
 #include "libavutil/opt.h"
 #include "libavutil/log.h"
 
-#ifndef __MAC_10_11
+#if __MAC_OS_X_VERSION_MIN_REQUIRED < 101100
 #define kAudioFormatEnhancedAC3 'ec-3'
 #endif