When expanding a MOVW (16-bit copy) to two MOVs (8-bit copy), the
lower byte always comes first. This is incorrect for corner cases like
'$r24r23 -> $r25r24', in which the higher byte copy should come first.
Current patch fixes that bug as recorded at
https://github.com/rust-lang/rust/issues/98167
Reviewed By: benshi001
Differential Revision: https://reviews.llvm.org/D128588
5650688e72