runtime/ReservedStack/ReservedStackTest* tests fail with 'This platform should not be supported: aarch64'

[smlambert]

On aarch64_windows, these 2 testcases fail:
runtime/ReservedStack/ReservedStackTest.java
runtime/ReservedStack/ReservedStackTestCompiler.java

with RuntimeException

FAILED: This platform should not be supported: aarch64
java.lang.RuntimeException: This platform should not be supported: aarch64
	at ReservedStackTest.initIsSupportedPlatform(ReservedStackTest.java:286)
	at ReservedStackTest.main(ReservedStackTest.java:291)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at com.sun.javatest.regtest.agent.MainWrapper$MainTask.run(MainWrapper.java:138)
	at java.base/java.lang.Thread.run(Thread.java:1583)