Fix folding of vector EQ/NE

Fix folding of vector EQ/NE

For vector1 != vector2, we returned false if any elements were equal,
rather than if all elements were equal.

2019-07-10  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* fold-const.c (fold_relational_const): Fix folding of
	vector-to-scalar NE_EXPRs.
	(test_vector_folding): Add more tests.

From-SVN: r273366