Use scan-tree-dump instead of scan-tree-dump-times for some vect tests

Use scan-tree-dump instead of scan-tree-dump-times for some vect tests

With later patches, we're able to vectorise the epilogues of these tests
on AArch64 and so get two instances of "vectorizing stmts using SLP".
Although it would be possible with a bit of effort to predict when
this happens, it doesn't seem important whether we get 1 vs. 2
occurrences.  All that matters is zero vs. nonzero.

2019-11-06  Richard Sandiford  <richard.sandiford@arm.com>

gcc/testsuite/
	* gcc.dg/vect/slp-9.c: Use scan-tree-dump rather than
	scan-tree-dump-times.
	* gcc.dg/vect/slp-widen-mult-s16.c: Likewise.
	* gcc.dg/vect/slp-widen-mult-u8.c: Likewise.

From-SVN: r277881