Fix some of vect-avg-*.c testcases

The vect-avg-*.c testcases are trying to make sure
the AVG internal function are used and not
doing promotion to `vector unsigned short`
but when V4QI is implemented, `vector(2) unsigned short`
shows up in the detail dump file and causes the failure.
To fix this checking the optimized dump instead of the vect dump
for `vector unsigned short` to make sure the vectorizer does not
do the promotion.

Built and tested for aarch64-linux-gnu.

gcc/testsuite/ChangeLog:

	* gcc.dg/vect/vect-avg-1.c: Check optimized dump
	for `vector *signed short` instead of the `vect` dump.
	* gcc.dg/vect/vect-avg-11.c: Likewise.
	* gcc.dg/vect/vect-avg-12.c: Likewise.
	* gcc.dg/vect/vect-avg-13.c: Likewise.
	* gcc.dg/vect/vect-avg-14.c: Likewise.
	* gcc.dg/vect/vect-avg-2.c: Likewise.
	* gcc.dg/vect/vect-avg-3.c: Likewise.
	* gcc.dg/vect/vect-avg-4.c: Likewise.
	* gcc.dg/vect/vect-avg-5.c: Likewise.
	* gcc.dg/vect/vect-avg-6.c: Likewise.
	* gcc.dg/vect/vect-avg-7.c: Likewise.
	* gcc.dg/vect/vect-avg-8.c: Likewise.

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