8234160: ZGC: Enable optimized mitigation for Intel jcc erratum in C2 load barrier

[Florian Weimer]

* Paul Hohensee:

> It's not just the zgc load barrier that's affected, it's every jcc and
> fuzed jcc (e.g., cmp/jcc and sub/jcc, because the pairs are issued on
> the same clock).

The microcode update reportedly affects all of JMP/Jcc/CALL/RET subject
to the alignment constraints, not just Jcc.  Therefore, mitigating the
performance impact and papering over the original issue require
different machine code.

Thanks,
Florian