hsx24 backport: Request for review: 7122222: GC log is limited to 2G for 32-bit

[Tao Mao]

The hsx25 fix has been pushed already. Then I got the 
7u40-critical-approved.

When I tried backporting to hsx24, it didn't apply to the hsx24 repo 
cleanly. Thus, I made the patch manually (copy-and-paste style) and now 
need some quick reviews to get it in since it's 7u40 related P3 CR.

hsx24 webrev:
http://cr.openjdk.java.net/~tamao/7122222_hsx24/webrev.00/

(original) hsx25 webrev:
http://cr.openjdk.java.net/~tamao/7122222/webrev.00/

Thanks.
Tao