amdgcn: Don't clobber VCC if we don't need to

amdgcn: Don't clobber VCC if we don't need to

This is a hold-over from GCN3 where v_add always wrote to the condition
register, whether you wanted it or not.  This hasn't been true since GCN5, and
we dropped support for GCN3 a little while ago, so let's fix it.

There was actually a latent bug here because some other post-reload splitters
were generating v_add instructions without declaring the VCC clobber (at least
mul did this), so this should fix some wrong-code bugs also.

gcc/ChangeLog:

	* config/gcn/gcn-valu.md (add<mode>3<exec_clobber>): Rename ...
	(add<mode>3<exec>): ... to this, remove the clobber, and change the
	instruction from v_add_co_u32 to v_add_u32.
	(add<mode>3_dup<exec_clobber>): Rename ...
	(add<mode>3_dup<exec>): ... to this, and likewise.
	(sub<mode>3<exec_clobber>): Rename ...
	(sub<mode>3<exec>): ... to this, and likewise
	* config/gcn/gcn.md (addsi3): Remove the DI clobber, and change the
	instruction from v_add_co_u32 to v_add_u32.
	(addsi3_scc): Likewise.
	(subsi3): Likewise, but for v_sub_co_u32.
	(muldi3): Likewise.

(cherry picked from commit 0eee2dd2865faf61d9d74425510421e20434ec03)