RFR: JDK-8222333: fastdebug build broken after JDK-8221393

[Ao Qi]

Hi,

Bugs:
https://bugs.openjdk.java.net/browse/JDK-8222333

Webrev:
http://cr.openjdk.java.net/~aoqi/8222333/webrev.00/

fastdebug build is broken after JDK-8221393. It seems that
phase_mapping[] doesn't match enum Phase in WeakProcessorPhases
anymore. Is this fix ok? I am not familiar with shenandoah.
linux-x86_64-server-release hotspot:tier1 tested.

Thanks,
Ao Qi