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

[Tim Bell]

Hi Mike:

> 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/

Looks good.

Tim