Similar to 806761a7629df268c8aed49657aeccffa6bca449
-mtriple= specifies the full target triple while -march= merely sets the
architecture part of the default target triple, leaving a target triple which
may not make sense.
Therefore, -march= is error-prone and not recommended for tests without a target
triple. The issue has been benign as we recognize avr-apple-darwin as ELF instead
of rejecting it outrightly.
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
