RFR: 8156759: [JVMCI] remove JVMCIError and UnsafeUtil classes

[Doug Simon]

Please review this change which removes a couple of classes which do not need to be in JVMCI.

I’ve also taken the liberty of including a change that updates the mx Java compliance level for all JVMCI projects to 9 since JDK9 API (e.g., java.lang.reflect.Module) is now used in JVMCI. This means building with mx has been broken since that API usage was introduced. I can pull this out into a separate RFE if necessary but am hoping it can piggy back on this bug.

https://bugs.openjdk.java.net/browse/JDK-8156759
http://cr.openjdk.java.net/~dnsimon/8156759

-Doug