Add more markup to vect-alias-check-{1,18}.c (PR 92543)

Add more markup to vect-alias-check-{1,18}.c (PR 92543)

In vect-alias-check-1.c we unroll the inner loop and then vectorise
the stores at a[c + 1][b].  Since the access has no guaranteed
alignemnt, we need a realignment mechanism or support for unaligned
accesses in order to vectorise.

In vect-alias-check-18.c we use a reverse access and so need
permute support in order to vectorise.

I'm not really sure when this part of the testsuite prefers
{ xfail { ! foo } } and when it prefers { target foo }.  xfail
seems like the most common choice for the alignment restriction,
whereas vect_int and vect_perm are mostly dg-require-effective-target
style features, so I went with that combination.

2019-11-21  Richard Sandiford  <richard.sandiford@arm.com>

gcc/testsuite/
	PR testsuite/92543
	* gcc.dg/vect/vect-alias-check-1.c: XFAIL the alias check message
	if there is no realignment support and no support for unaligned
	accesses.
	* gcc.dg/vect/vect-alias-check-18.c: Restrict the test for the
	alias message to targets that have permute support.

From-SVN: r278591