RFR(S) 8023003: Cleanup the public interface to PhaseCFG

[Niclas Adlertz]

Hi all,

a review would be much appreciated. 
The main changes for this patch are located in block.hpp, gcm.cpp and compile.cpp. 

WEBREV: http://cr.openjdk.java.net/~adlertz/JDK-8023003/webrev00/
JBS: https://jbs.oracle.com/bugs/browse/JDK-8023003


Kind Regards,
Niclas Adlertz