RFR: Fix LRB use in LIRGenerator::do_UnsafeGetAndSetObject (Aarch64 attendum)

[Roman Kennke]

>> This fixes the same C1 getAndSetObject() problem that Aleksey recently
>> fixed in x86, but for aarch64:
>>
>> http://cr.openjdk.java.net/~rkennke/shjdk8-aarch64-xchg/webrev.00/
> 
> You sure the destination is on the right? This is the same C1 LIR, so it should match x86? If so,
> looks good.

Yes, see here:
http://hg.openjdk.java.net/shenandoah/jdk8/hotspot/file/851f16923028/src/share/vm/c1/c1_LIR.hpp#l2115

It is one of the weird quirks of C1 that it works the other direction
compared to OpenJDK's asm.

See also the x86 change:
http://hg.openjdk.java.net/shenandoah/jdk8/hotspot/rev/cf0f69f962d9

> It is "addendum". Better yet:
>  AArch64: Fix LRB use in LIRGenerator::do_UnsafeGetAndSetObject

Ok, will push under this synopsis.

Thank you,
Roman