Win8365790Test cannot find the class "SkippedException" in versions of jtreg under 7.5.1+1.

I propose adding the following two lines to the top of that class to enable this test to be compatible with earlier versions of jtreg.

* @library /test/lib
* @build jtreg.SkippedException

This has been tested on one of our machines and seems to work well.
Test configs:
- JDK17 - jtreg 7.3.1+1
- JDK25 - jtreg 7.5.1+1