[10] RFR(M): 8176506: C2: loop unswitching and unsafe accesses cause crash

[Roland Westrelin]

> X86 Manual says:
>
> "Use the 0F0B opcode (UD2 instruction) or the 0FB9H opcode when 
> deliberately trying to generate an invalid opcode exception (#UD)."

Thanks, Vladimir.

Here is a new webrev. Halt now should trigger a SIGILL on all
platforms. I tested x86, aarch64, arm64. The code for arm32 needs to be
tested (I can't even build on arm32).

http://cr.openjdk.java.net/~roland/8176506/webrev.04/

Roland.