rs6000: Use rs6000_emit_move in movmisalign<mode> expander [PR104681]

rs6000: Use rs6000_emit_move in movmisalign<mode> expander [PR104681]

The following testcase ICEs, because for some strange reason it decides to use
movmisaligntf during expansion where the destination is MEM and source is
CONST_DOUBLE.  For normal mov<mode> expanders the rs6000 backend uses
rs6000_emit_move to ensure that if one operand is a MEM, the other is a REG
and a few other things, but for movmisalign<mode> nothing enforced this.
The middle-end documents that movmisalign<mode> shouldn't fail, so we can't
force that through predicates or condition on the expander.

2022-02-25  Jakub Jelinek  <jakub@redhat.com>

	PR target/104681
	* config/rs6000/vector.md (movmisalign<mode>): Use rs6000_emit_move.

	* g++.dg/opt/pr104681.C: New test.

(cherry picked from commit 3885a122f817a1b6dca4a84ba9e020d5ab2060af)