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

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)
```

Start with runtime/ReservedStack/ReservedStackTest.java and runtime/ReservedStack/ReservedStackTestCompiler.java, especially initIsSupportedPlatform at line 286. Run both tests on aarch64_windows and inspect how the platform check handles aarch64. Done means the tests no longer fail with the unsupported-platform exception.

Written by the indexing model from the issue text.