arm: intreadwrite: disable inline asm for gcc 4.7 and later

Starting with version 4.7, gcc properly supports unaligned
memory accesses on ARM.  Not using the inline asm with these
compilers results in better code.
Signed-off-by: Mans Rullgard <mans@mansr.com>

libavutil/arm/intreadwrite.h

@@ -21,8 +21,9 @@
 
 #include <stdint.h>
 #include "config.h"
+#include "libavutil/attributes.h"
 
-#if HAVE_FAST_UNALIGNED && HAVE_INLINE_ASM
+#if HAVE_FAST_UNALIGNED && HAVE_INLINE_ASM && !AV_GCC_VERSION_AT_LEAST(4,7)
 
 #define AV_RN16 AV_RN16
 static av_always_inline unsigned AV_RN16(const void *p)