[foreign-abi] RFR 8229918: Fix clash between recent CallingSequenceTest patch and Windows varargs support patch

[Jorn Vernee]

Hi,

Please review this small fix that fixes a conflict between 2 recent patches.

Bug: https://bugs.openjdk.java.net/browse/JDK-8229918
Webrev: 
http://cr.openjdk.java.net/~jvernee/panama/webrevs/8229918/webrev.00/

Thanks,
Jorn