[aarch64-port-dev ] RFR (trivial): 8219698: aarch64: SIGILL triggered when specifying unsupported hardware features

[Yangfei (Felix)]

Hi,

    Please review this trivial patch.  
    Bug: https://bugs.openjdk.java.net/browse/JDK-8219698
    Webrev: http://cr.openjdk.java.net/~fyang/8219698/webrev.00/
    
    Verified the SIGILL will not trigger with this fix.  OK to push?  

Thanks,
Felix