RFR(XS): JDK-8077315 - Build failure on OSX after compiler upgrade

[Jesper Wilhelmsson]

Hi,

Please review this minor fix to move the declaration of always_contains in 
instanceRefKlass.inline.hpp

The current declaration caused problems with -Wunneeded-internal-declaration 
after the compiler upgrade on OSX.

Bug: https://bugs.openjdk.java.net/browse/JDK-8077315
Webrev: http://cr.openjdk.java.net/~jwilhelm/8077315/

Since this is a minor fix and it is blocking pushes to the GC repository I would 
prefer not to wait 24 hours to push this.

Thanks,
/Jesper