32-bit build is broken

[David Holmes]

FYI the 32-bit build is broken after:

"8230594: Allow direct handshakes without VMThread intervention"

we forgot about this restriction:

   // Atomic operations on int64 types are not available on all 32-bit
   // platforms. If atomic ops on int64 are defined here they must only
   // be used from code that verifies they are available at runtime and
   // can provide an alternative action if not - see supports_cx8() for
   // a means to test availability.

and added a 64-bit atomic counter.

https://bugs.openjdk.java.net/browse/JDK-8237753

David