ARM: first value loaded in AV_RN64 needs to be early-clobber
Originally committed as revision 19656 to svn://svn.ffmpeg.org/ffmpeg/trunk
ARM asm for AV_RN*()
ARMv6 and later support unaligned loads and stores for singleword/halfword but not double/multiple. GCC is ignorant of this andwill always use bytewise accesses for unaligned data. Casting to anint32_t pointer is dangerous since a load/store double or multiple...