RFR(XS) Fixed calling convention of shenandoah_wb() C entry on Windows

[Aleksey Shipilev]

On 07/26/2017 09:31 PM, Zhengyu Gu wrote:
> On Windows with VS, the first argument is passed in RCX instead of RDI (Linux/gcc). There is the VS
> 2015 document: https://msdn.microsoft.com/en-us/library/9z1stfyw.aspx
> 
> 
> Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/windows_c_call/webrev.00/

I assumed it was an overlook not to push the backport to 8u, but only to 9? Pushed to 8u too:
  http://hg.openjdk.java.net/shenandoah/jdk8u/hotspot/rev/0ed2d40236c2

-Aleksey