[11u] RFR/RFC: Backport the remaining test for JDK-8220714

[Aleksey Shipilev]

We have a special bug:
 https://bugs.openjdk.java.net/browse/JDK-8220714

It has shared fix, backported to 11.0.4, and we got it in sh/jdk11 with regular merge. And there is
Shenandoah-specific test that was obviously missing in upstream backports, and we need to backport
it separately. This is it:

$ hg qdiff --stat
 test/hotspot/jtreg/gc/shenandoah/compiler/TestUnsafeOffheapSwap.java |  109
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 109 insertions(+), 0 deletions(-)

[backport] 8220714: C2 Compilation failure when accessing off-heap memory using Unsafe
Reviewed-by: vlivanov, roland

$ hg export
--- /dev/null   Thu Jan 01 00:00:00 1970 +0000
+++ b/test/hotspot/jtreg/gc/shenandoah/compiler/TestUnsafeOffheapSwap.java      Fri Mar 15 09:57:42
2019 +0100
@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2019, Red Hat, Inc. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
...

Testing: new test, with/without Graal

-- 
Thanks,
-Aleksey