RFR 8203466: intermittent crash at jdk.internal.misc.Unsafe::getObjectVolatile (native)

[coleen.phillimore at oracle.com]

Summary: Save windows 64 callee saved registers rsi, rdi to Thread, save 
r15, also callee saved to r9

This is done for generated stubs that do arraycopy that need GC barrier 
code because GC assumes that r10 is scratch, since it's defined as 
rscratch1.  See bug for more details.  Thanks Erik for your help and the 
diagnosis.

Tested with mach5 hs-tier1-7.  We don't have a reproduceable test case.

open webrev at http://cr.openjdk.java.net/~coleenp/8203466.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8203466

Thanks,
Coleen