SHA256RNDS2/MSG1/MSG2 with a memory source made `--to-intel` fail the
whole relink. The stub now spills a scratch xmm, loads the operand into
it with MOVDQU (AMD does not fault on a misaligned SHA operand, so the
unaligned load keeps that behaviour) and runs the register-form
lowering. RSP-based operands get the spill depth added to their
displacement. RIP-relative operands still fail: the stub runs at a
different address.
Co-Authored-By: Claude <noreply@anthropic.com>