vec-lowering: Fix ABSU lowering [PR111285]

vec-lowering: Fix ABSU lowering [PR111285]

ABSU_EXPR lowering incorrectly used the resulting type
for the new expression but in the case of ABSU the resulting
type is an unsigned type and with ABSU is folded away. The fix
is to use a signed type for the expression instead.

Bootstrapped and tested on x86_64-linux-gnu.

	PR middle-end/111285

gcc/ChangeLog:

	* tree-vect-generic.cc (do_unop): Use a signed type for the
	operand if the operation was ABSU_EXPR.

gcc/testsuite/ChangeLog:

	* g++.dg/torture/vect-absu-1.C: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>