intreadwrite: Use __unaligned in MSVC for ARM64 as well

This attribute is supported for this architecture in MSVC as well
(but produces errors if used for 32 bit x86).
Signed-off-by: Martin Storsjö <martin@martin.st>

libavutil/intreadwrite.h

@@ -192,7 +192,7 @@ union unaligned_16 { uint16_t l; } __attribute__((packed)) av_alias;
 #   define AV_RN(s, p) (((const union unaligned_##s *) (p))->l)
 #   define AV_WN(s, p, v) ((((union unaligned_##s *) (p))->l) = (v))
 
-#elif defined(_MSC_VER) && (defined(_M_ARM) || defined(_M_X64)) && AV_HAVE_FAST_UNALIGNED
+#elif defined(_MSC_VER) && (defined(_M_ARM) || defined(_M_X64) || defined(_M_ARM64)) && AV_HAVE_FAST_UNALIGNED
 
 #   define AV_RN(s, p) (*((const __unaligned uint##s##_t*)(p)))
 #   define AV_WN(s, p, v) (*((__unaligned uint##s##_t*)(p)) = (v))