The second loop in the testcase only vectorises if we can reverse
a vector and if aligned loads aren't required.

2017-08-10  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/testsuite/
	PR testsuite/81738
	* gcc.dg/vect/vect-alias-check-6.c: Move second function to...
	* gcc.dg/vect/vect-alias-check-7.c: ...this new file.  Require
	vect_perm and vect_element_align for vectorization.

From-SVN: r251037