RFR(S) 8234432: AOT tests failing with 'used 'epsilon gc' is different from current 'g1 gc'' after CMS removal

[Dean Long]

https://bugs.openjdk.java.net/browse/JDK-8234432
http://cr.openjdk.java.net/~dlong/8234432/webrev/

The change fixes AOT after CMS was removed.  Previously we relied to a 
Graal enum matching a JDK enum, but now we map from one to the other.

dl