RFR(S): Atomic::add() with 64 bit value fails to link on 32-bit platforms

[Markus Gronlund]

Greetings,

This is a follow-up fix to address a build (link) issue on 32-bit platforms introduced by https://bugs.openjdk.java.net/browse/JDK-8242088  

Bug: https://bugs.openjdk.java.net/browse/JDK-8246770 
Webrev: http://cr.openjdk.java.net/~mgronlun/8246770/webrev00/ 
Testing: building 32-bits

Thanks
Markus