Disable epilogue loop vectorisation for vect-widen-mult-u8-*.c

Disable epilogue loop vectorisation for vect-widen-mult-u8-*.c

vect-widen-mult-u8.c and vect-widen-mult-u8-u32.c were failing
on arm-linux-gnueabihf with epilogue vectorisation because we
print the expected messages twice rather than once.  We could
fix that either by removing the counts or by disabling epilogue
loop vectorisation.  The other vect-widen-mult-* tests do the
latter, so I did the same here.

2019-11-22  Richard Sandiford  <richard.sandiford@arm.com>

gcc/testsuite/
	* gcc.dg/vect/vect-widen-mult-u8.c: Disable epilogue loop
	vectorization.
	* gcc.dg/vect/vect-widen-mult-u8-u32.c: Likewise.

From-SVN: r278613