RFR(XS): 7193946: Move warnings associated with UseMemSetInBOT flag

[John Cuthbertson]

Hi Everyone,

Can I have a couple of volunteers review the changes for this CR? They 
are fairly small. The webrev can be found at: 
http://cr.openjdk.java.net/~johnc/7193946/webrev.0/

Summary:
In the review comments for the fix for 7192128, Bengt suggested to move 
the individual warnings from concurrentMarkSweepGeneration.cpp and 
g1Collectedheap.cpp and place a single warning in a common piece of 
code. These changes address that review comment. The suggested location 
(vm_version_sparc.cpp) was unsuitable as the routine which would be the 
natural choice is called twice and the warning would be issued twice. A 
better place is when we check the other GC flags for consistency in 
arguments.cpp.

Testing:
* command line testing
* GC basher and GCOld on sun4v with and without UseMemSetInBOT set

Thanks,

JohnC