RFR :8014269: (XXS) Add missing .PHONY targets to Main.gmk

[Mike Duigou]

Hello all;

Small issue for review. Some of the Main.gmk targets aren't mentioned in the 
PHONY targets as they should be.

http://cr.openjdk.java.net/~mduigou/JDK-8014269/0/webrev/

Mike