RFR: 8189333: Fix Zero build after Atomic::xchg changes

[Roman Kennke]

Zero debug build has been broken by: JDK-8187977: Generalize 
Atomic::xchg to use templates.

This patch fixes it by casting the unsigned literal to jint:

http://cr.openjdk.java.net/~rkennke/8189333/webrev.00/ 
<http://cr.openjdk.java.net/%7Erkennke/8189333/webrev.00/>

Tested by building zero fastdebug and running some small test programs.

Ok?


Roman