RFR: Fix up pointer volatility

[Aleksey Shipilev]

Hi,

Scanned through our changes against upstream to see if we get pointer volatility
right everywhere. We seem to be, and the only missing place is this:

diff -r 71ef78a756e7 src/share/vm/gc/shenandoah/shenandoahHeap.hpp
--- a/src/share/vm/gc/shenandoah/shenandoahHeap.hpp	Fri May 12 12:51:33 2017 +0200
+++ b/src/share/vm/gc/shenandoah/shenandoahHeap.hpp	Fri May 12 13:21:39 2017 +0200
@@ -201,7 +201,7 @@
   ShenandoahConnectionMatrix* _connection_matrix;

 #ifdef ASSERT
-  volatile Thread* _heap_lock_owner;
+  Thread* volatile _heap_lock_owner;
 #endif

 public:

Testing: hotspot_gc_shenandoah

Thanks,
-Aleksey