8234822: Limit ZGC jtreg-support to Windows 2019 Server

Reviewed-by: iignatyev, eosterlund

test/lib/sun/hotspot/gc/GC.java

@@ -48,11 +48,28 @@ public enum GC {
         this.name = name;
     }
 
+    private boolean supportsOSVersion() {
+        if (this != Z) {
+            return true;
+        }
+
+        String osName = System.getProperty("os.name");
+
+        if (!osName.startsWith("Windows")) {
+            return true;
+        }
+
+        // ZGC has specific Windows version requirements (>= 1803).
+        // The following check should be made more precise to
+        // also catch the corresponding Windows 10 version.
+        return osName.equals("Windows Server 2019");
+    }
+
     /**
      * @return true if this GC is supported by the VM, i.e., it is built into the VM.
      */
     public boolean isSupported() {
-        return WB.isGCSupported(name);
+        return WB.isGCSupported(name) && supportsOSVersion();
     }
 
     /**