RFR: 8234619: ZGC: gc/z/TestSmallHeap.java failure with Out Of Memory

[Per Liden]

The test gc/z/TestSmallHeap.java sometimes fails when run with and 
-Xcomp. As it turns out, about 120K worth of additional intern Strings 
are created when running with -Xcomp. On an 8M heap, means there's not 
enough room left for the 512K array allocation this test does. This 
patch simply disables this test when using -Xcomp.

Bug: https://bugs.openjdk.java.net/browse/JDK-8234619
Webrev: http://cr.openjdk.java.net/~pliden/8234619/webrev.0

Testing: Manual runs with gc/z/TestSmallHeap.java

/Per