RFR: 8187315: [JVMCI] remove unnecessary synchronization

[dean.long at oracle.com]

Looks reasonable.  Subject line is out of sync with bug title: [JVMCI] 
hosted use of JVMCI can crash VM under -Xint

dl


On 11/3/17 10:42 AM, Doug Simon wrote:
> Please review this small change to fix a crash when using Graal in hosted-only mode.
>
> https://bugs.openjdk.java.net/browse/JDK-8187315
> http://cr.openjdk.java.net/~dnsimon/8187315/
>
> -Doug