RF(XS): 8154939: 8153998 broke vectorization on aarch64

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8154939/webrev.00/

8153998 added a test that assumes SuperWordLoopUnrollAnalysis is enabled
but it's not the case on aarch64. As a consequence, vectorization
doesn't trigger on aarch64 anymore.

Roland.